Response to early literacy instruction in the United States, Australia, and Scandinavia: A behavioral-genetic analysis

Addressing genetic essentialism: Sharpening context in behavior genetics

Evidence of a causal role for genes in human behavior underpins genetic essentialism, the scientifically flawed and socially hazardous idea that heritable characteristics are immutable. Behavior geneticists can challenge this idea by designing research that brings the contextual dependence of heritability estimates into sharper focus, and by incorporating a relevant statement into research reports and public outreach.

Joint Consideration of Means and Variances Might Change the Understanding of Etiology

Twin and adoption studies compare the similarities of people with differing degrees of relatedness to estimate genetic and environmental contributions to trait population variance. The analytic workhorse of these kinds of variance-focused designs is the intraclass correlation, which estimates similarity between pairs of individuals. Group means, by contrast, play no overt role in estimating genetic and environmental influences. Although this focus on variance has made very important contributions to understanding psychological characteristics, we contend that the exclusion of mean effects from behavioral genetic designs may have obscured key environmental influences and impeded full appreciation of the ubiquity and nature of gene-environment interplay in human outcomes. We provide empirical examples already in the literature and a theoretical framework for thinking through the incorporation of mean effects using largely forgotten, non-Mendelian theory regarding how genes influence human outcomes. We conclude that the field needs to develop models capable of fully incorporating mean effects into twin and adoption studies.

Orthographic Depth May Influence the Degree of Severity of Maze Learning Performance in Children at Risk for Reading Disorder

Reading disability (RD), which affects between 5 and 17% of the population worldwide, is the most prevalent form of learning disability, and is associated with underactivation of a universal reading network in children. However, recent research suggests there are differences in learning rates on cognitive predictors of reading performance, as well as differences in activation patterns within the reading neural network, based on orthographic depth (i.e., transparent/shallow vs. deep/opaque orthographies) in children with RD. Recently, we showed that native English-speaking children with RD exhibit impaired performance on a maze learning task that taps into the same neural networks that are activated during reading. In addition, we demonstrated that genetic risk for RD strengthens the relationship between reading impairment and maze learning performance. However, it is unclear whether the results from these studies can be broadly applied to children from other language orthographies. In this study, we examined whether low reading skill was associated with poor maze learning performance in native English-speaking and native German-speaking children, and the influence of genetic risk for RD on cognition and behavior. In addition, we investigated the link between genetic risk and performance on this task in an orthographically diverse sample of children attending an English-speaking international school in Germany. The results from our data suggest that children with low reading skill, or with a genetic risk for reading impairment, exhibit impaired performance on the maze learning task, regardless of orthographic depth. However, these data also suggest that orthographic depth influences the degree of impairment on this task. The maze learning task requires the involvement of various cognitive processes and neural networks that underlie reading, but is not influenced by potential differences in reading experience due to lack of text or oral reporting. As a fully automated tool, it does not require specialized training to administer, and current results suggest it may be a practicable screening tool for early identification of reading impairment across orthographies.

Evolving the blank slate

We support Uchiyama et al. in the value of genetics, sample diversification, and context measurement. Against the example of vitamins, we highlight the intransigence of many phenotypes. We caution that while culture can mask genetic differences, the dependence of behaviour on genetics is reinvented and unmasked by novel challenges across generations.

Unpackaging cultural variability in behavioral phenotypes

We need better understanding of functional differences of behavioral phenotypes across cultures because cultural evolution (e.g., temporal changes in innovation within populations) is less important than culturally molded phenotypes (e.g., differences across populations) for understanding gene effects. Furthermore, changes in one behavioral domain likely have complex downstream effects in other domains, requiring careful parsing of phenotypic variability and functions.

The Genetic, Environmental, and Cultural Forces Influencing Youth Antisocial Behavior Are Tightly Intertwined

The aggressive and rule-breaking behaviors that constitute youth antisocial behavior (ASB) are shaped by intertwined genetic, developmental, familial, spatial, temporal, cultural, interpersonal, and contextual influences operating across multiple levels of analysis. Genetic influences on ASB, for example, manifest in different ways during different developmental periods, and do so in part as a function of exposure to harsh parenting, delinquent peers, and disadvantaged neighborhoods. There is also clear evidence documenting societal effects, time-period effects, sex-assigned-at-birth effects, and cohort effects, all of which point to prominent (and possibly interconnected) cultural influences on ASB. In short, ASB is shaped by individuals' current and prior environmental experiences, genetic risks, and the time and place in which they live. This review seeks to illuminate already documented instances of interplay among the multilevel etiologic forces impinging on youth ASB, with the goal of facilitating additional research.

The developmental origins of genetic factors influencing language and literacy: Associations with early-childhood vocabulary

BACKGROUND

The heritability of language and literacy skills increases from early-childhood to adolescence. The underlying mechanisms are little understood and may involve (a) the amplification of genetic influences contributing to early language abilities, and/or (b) the emergence of novel genetic factors (innovation). Here, we investigate the developmental origins of genetic factors influencing mid-childhood/early-adolescent language and literacy. We evaluate evidence for the amplification of early-childhood genetic factors for vocabulary, in addition to genetic innovation processes.

METHODS

Expressive and receptive vocabulary scores at 38 months, thirteen language- and literacy-related abilities and nonverbal cognition (7-13 years) were assessed in unrelated children from the Avon Longitudinal Study of Parents and Children (ALSPAC, N_individuals  ≤ 6,092). We investigated the multivariate genetic architecture underlying early-childhood expressive and receptive vocabulary, and each of 14 mid-childhood/early-adolescent language, literacy or cognitive skills with trivariate structural equation (Cholesky) models as captured by genome-wide genetic relationship matrices. The individual path coefficients of the resulting structural models were finally meta-analysed to evaluate evidence for overarching patterns.

RESULTS

We observed little support for the emergence of novel genetic sources for language, literacy or cognitive abilities during mid-childhood or early adolescence. Instead, genetic factors of early-childhood vocabulary, especially those unique to receptive skills, were amplified and represented the majority of genetic variance underlying many of these later complex skills (≤99%). The most predictive early genetic factor accounted for 29.4%(SE = 12.9%) to 45.1%(SE = 7.6%) of the phenotypic variation in verbal intelligence and literacy skills, but also for 25.7%(SE = 6.4%) in performance intelligence, while explaining only a fraction of the phenotypic variation in receptive vocabulary (3.9%(SE = 1.8%)).

CONCLUSIONS

Genetic factors contributing to many complex skills during mid-childhood and early adolescence, including literacy, verbal cognition and nonverbal cognition, originate developmentally in early-childhood and are captured by receptive vocabulary. This suggests developmental genetic stability and overarching aetiological mechanisms.

Differential Patterns of Growth in Reading and Math Skills during Elementary School

This study investigated developmental trajectories of reading and math using latent-growth-curve analyses across multiple academic skills, measures, and multiple time periods within a single sample. Reading-related growth was marked by significant individual differences during the early elementary-school period and non-significant individual differences during the late elementary-school period. For math-related skills, non-significant individual differences were present for early math growth and significant individual differences were present in late elementary-school. No clear pattern of cumulative, compensatory, or stable development emerged for either reading-related or math skills. These differing growth patterns highlight developmental complexities and suggest domain-specific differences in achievement growth that are potentially associated with contextual factors.

Cultural Evolution of Genetic Heritability

Behavioral genetics and cultural evolution have both revolutionized our understanding of human behavior-largely independent of each other. Here we reconcile these two fields under a dual inheritance framework, offering a more nuanced understanding of the interaction between genes and culture. Going beyond typical analyses of gene-environment interactions, we describe the cultural dynamics that shape these interactions by shaping the environment and population structure. A cultural evolutionary approach can explain, for example, how factors such as rates of innovation and diffusion, density of cultural sub-groups, and tolerance for behavioral diversity impact heritability estimates, thus yielding predictions for different social contexts. Moreover, when cumulative culture functionally overlaps with genes, genetic effects become masked, unmasked, or even reversed, and the causal effects of an identified gene become confounded with features of the cultural environment. The manner of confounding is specific to a particular society at a particular time, but a WEIRD (Western, educated, industrialized, rich, democratic) sampling problem obscures this boundedness. Cultural evolutionary dynamics are typically missing from models of gene-to-phenotype causality, hindering generalizability of genetic effects across societies and across time. We lay out a reconciled framework and use it to predict the ways in which heritability should differ between societies, between socioeconomic levels and other groupings within some societies but not others, and over the life course. An integrated cultural evolutionary behavioral genetic approach cuts through the nature-nurture debate and helps resolve controversies in topics such as IQ.

Comment on Asbury and Wai (2019), "Viewing education policy through a genetic lens," Journal of School Choice

Asbury and Wai (Journal of School Choice, 2019) perform a valuable service by summarizing much available behavior--genetic research on academic achievement. However they consider that no specific policies stem from the research body at this time. Here we do propose a policy based on some of our research using twins, namely that available funding for students struggling with learning to read be targeted to them individually rather than allocated to schools per se. We briefly canvass some practical issues, such as the variety of funding mechanisms, best-practice intervention techniques, and identification of struggling readers. We also outline a general research strategy for uncovering factors contributing to educational attainment that takes behavior-genetic research as its starting point and drills down from there, and advocate including genetically-sensitive methods in a growing list of quantitative research techniques in education.

The Academic Development Study of Australian Twins (ADSAT): Research Aims and Design

The Academic Development Study of Australian Twins was established in 2012 with the purpose of investigating the relative influence of genes and environments in literacy and numeracy capabilities across two primary and two secondary school grades in Australia. It is the first longitudinal twin project of its kind in Australia and comprises a sample of 2762 twin pairs, 40 triplet sets and 1485 nontwin siblings. Measures include standardized literacy and numeracy test data collected at Grades 3, 5, 7 and 9 as part of the National Assessment Program: Literacy and Numeracy. A range of demographic and behavioral data was also collected, some at multiple longitudinal time points. This article outlines the background and rationale for the study and provides an overview for the research design, sample and measures collected. Findings emerging from the project and future directions are discussed.

Differential Influences of Genes and Environment Across the Distribution of Reading Ability

We partitioned early childhood reading into genetic and environmental sources of variance and examined the full distribution of ability levels from low through normal to high as computed by quantile regression. The full sample comprised twin pairs measured at preschool (n = 977), kindergarten (n = 1028), grade 1 (n = 999), and grade 2 (n = 1000). Quantile regression analyses of the full distribution of literacy ability showed genetic influence in all grades from preschool to grade 2. At preschool, the low end of the distribution had higher genetic influence than the high end of the distribution and the shared environment influence was the opposite. These shared environment influences of preschool became insignificant with formal schooling. This suggests that higher scores in pre-literacy skills (preschool) are more influenced by shared environment factors, though these are short-lived. This study discusses the factors that may be influencing the results.

A Meta-Analytical Review of the Genetic and Environmental Correlations between Reading and Attention-Deficit Hyperactivity Disorder Symptoms and Reading and Math

According to the Multiple Deficit Model, comorbidity results when the genetic and environmental risk factors that increase the liability for a disorder are domain-general. In order to explore the role of domain-general etiological risk factors in the co-occurrence of learning-related difficulties, the current meta-analysis compiled 38 studies of third through ninth-grade children to estimate the average genetic, shared environmental, and nonshared environmental correlations between reading and attention-deficit/hyperactivity disorder (ADHD) symptoms, and reading and math, as well as their potential moderators. Results revealed average genetic, shared and nonshared environmental correlations between reading and ADHD symptoms of .42, .64, and .20, and reading and math of .71, .90, and .56, suggesting that reading and math may have more domain-general risk factors than reading and ADHD symptoms. A number of significant sources of heterogeneity were also found and discussed. These results have important implications for both intervention and classification of learning disabilities.

The genetic architecture of oral language, reading fluency, and reading comprehension: A twin study from 7 to 16 years

This study examines the genetic and environmental etiology underlying the development of oral language and reading skills, and the relationship between them, over a long period of developmental time spanning middle childhood and adolescence. It focuses particularly on the differential relationship between language and two different aspects of reading: reading fluency and reading comprehension. Structural equation models were applied to language and reading data at 7, 12, and 16 years from the large-scale TEDS twin study. A series of multivariate twin models show a clear patterning of oral language with reading comprehension, as distinct from reading fluency: significant but moderate genetic overlap between oral language and reading fluency (genetic correlation r_g = .46-.58 at 7, 12, and 16) contrasts with very substantial genetic overlap between oral language and reading comprehension (r_g = .81-.87, at 12 and 16). This pattern is even clearer in a latent factors model, fit to the data aggregated across ages, in which a single factor representing oral language and reading comprehension is correlated with-but distinct from-a second factor representing reading fluency. A distinction between oral language and reading fluency is also apparent in different developmental trajectories: While the heritability of oral language increases over the period from 7 to 12 to 16 years (from h² = .27 to .47 to .55), the heritability of reading fluency is high and largely stable over the same period of time (h² = .73 to .71 to .64). (PsycINFO Database Record

GENES AND GINI: WHAT INEQUALITY MEANS FOR HERITABILITY

Research has established that genetic differences among people explain a greater or smaller proportion of the variation in life outcomes in different environmental conditions. This review evaluates the results of recent educationally relevant behavioural genetic studies and meta-analyses in the context of recent trends in income and wealth distribution. The pattern of results suggests that inequality and social policies can have profound effects on the heritability of educational attainment and achievement in a population (Gene–Gini interplay). For example, heritability is generally higher at greater equality levels, suggesting that inequality stifles the expression of educationally relevant genetic propensities. The review concludes with a discussion of the mechanisms of Gene–Gini interplay and what the findings mean for efforts to optimize education for all people.

The Effects of Genetic and Environmental Factors on Writing Development

Researchers have identified sources of individual differences in writing across beginning and developing writers. The aim of the present study was to further clarify the sources of this variability by investigating the extent to which there are differences in genetic and environmental factors underlying the associations between lexical diversity, syntactic knowledge, and semantic cohesion knowledge in relation to writing. Differences were examined across two developmental phases of writing: beginning (i.e., elementary school) and developing (i.e., middle school). Participants included 262 twin pairs (Mage = 10.88 years) in elementary school and 247 twin pairs (Mage = 13.21 years) in middle school. Twins were drawn from the Florida Twin Project on Reading, Behavior, and Environment. Biometric models were conducted separately for subgroups defined by phase of writing development. Results indicated significant etiological differences in writing components across the two phases, such that effects associated with genes and non-shared environment were greater while effects associated with shared environment were lower in developing writers as compared to beginning writers. Furthermore, results showed that child-specific environment was the largest contributor to individual differences in writing components and their covariation for both beginning and developing writers. These results imply that even direct instruction about writing in schools may be having different effects on children based on their unique experiences.

Patterns of biomarkers for three phenotype profiles of persisting specific learning disabilities during middle childhood and early adolescence: A preliminary study

Students without specific learning disabilities [SLDs] [n=18] and with one of three persisting SLDs in written language despite early and current specialized instruction-Dysgraphia [n=21], Dyslexia [n=40], or oral and written language learning disability OWL LD [n=14]- in grades 4 to 9 [N=56 boys, 38 girls] completed behavioral phenotyping assessment and gave a small blood or saliva sample. Molecular analyses informed by current cross-site research on gene candidates for learning disabilities identified associations between molecular genetic markers and the two defining behavioral phenotypes for each SLDs-WL; dysgraphia [impaired writing alphabet from memory for rs3743204 and sentence copying in best handwriting for rs79382 both in DYX1C1], dyslexia [impaired silent word reading/decoding rate for rs4535189 in DCDC2 and impaired spelling/encoding for rs374205 in DYX1C1], and OWL LD [impaired aural syntax comprehension for rs807701 and oral syntax construction for rs807701 both in DYX1C1]. Implications of these identified associations between molecular markers for alleles for different sites within two gene candidates [and mostly one] and hallmark phenotypes are discussed for translation science [application to practice] and neuroimaging that has identified contrasting brain bases for each of the three SLDs.

Genetic transmission of reading ability

Reading is the processing of written language. Family resemblance for reading (dis)ability might be due to transmission of a genetic liability or due to family environment, including cultural transmission from parents to offspring. Familial-risk studies exploring neurobehavioral precursors for dyslexia and twin studies can only speak to some of these issues, but a combined twin-family study can resolve the nature of the transmitted risk. Word-reading fluency scores of 1100 participants from 431 families (with twins, siblings and their parents) were analyzed to estimate genetic and environmental sources of variance, and to test the presence of assortative mating and cultural transmission. Results show that variation in reading ability is mainly caused by additive and non-additive genetic factors (64%). The substantial assortative mating (r_{father-mother}=0.38) has scientific and clinical implications. We conclude that parents and offspring tend to resemble each other for genetic reasons, and not due to cultural transmission.

Longitudinal Stability and Growth in Literacy and Numeracy in Australian School Students

We explored the genetic and environmental influence on both stability and growth in literacy and numeracy in 1927 Australian twin pairs from Grade 3 to Grade 9. Participants were tested on reading, spelling, grammar and punctuation, writing, and numeracy. In each domain, performance across time was highly correlated and this stability in performance was primary due to genes. Key findings on growth showed that reading followed a compensatory growth pattern that was largely due to genetic effects, while variation in growth in the other literacy domains was predominantly due to environmental influences. Genes and the shared environment influenced growth in numeracy for girls, while for boys it was influenced by the shared and unique environment. These results suggest that individual differences in growth of reading are primarily due to a genetically influenced developmental delay in the acquisition of necessary skills, while environmental influences, perhaps including different schools or teachers, are more important for the other domains.

Arithmetic, reading and writing performance has a strong genetic component: A study in primary school children

Even children attending the same primary school and taught by the same teacher differ greatly in their performance. In the Netherlands, performance at the end of primary school determines the enrollment in a particular level of secondary education. Identifying the impact of genes and the environment on individual differences in educational achievement between children is important. The Netherlands Twin Register has collected data on scores of tests used in primary school (ages 6 to 12) to monitor a child's educational progress in four domains, i.e. arithmetic, word reading, reading comprehension and spelling (1058 MZ and 1734 DZ twin pairs), and of a final test (2451 MZ and 4569 DZ twin pairs) in a large Dutch cohort. In general, individual differences in educational achievement were to a large extent due to genes and the influence of the family environment was negligible. Moreover, there is no evidence for gender differences in the underlying etiology.

Evidence-Based Reading and Writing Assessment for Dyslexia in Adolescents and Young Adults

The same working memory and reading and writing achievement phenotypes (behavioral markers of genetic variants) validated in prior research with younger children and older adults in a multi-generational family genetics study of dyslexia were used to study 81 adolescent and young adults (ages 16 to 25) from that study. Dyslexia is impaired word reading and spelling skills below the population mean and ability to use oral language to express thinking. These working memory predictor measures were given and used to predict reading and writing achievement: Coding (storing and processing) heard and spoken words (phonological coding), read and written words (orthographic coding), base words and affixes (morphological coding), and accumulating words over time (syntax coding); Cross-Code Integration (phonological loop for linking phonological name and orthographic letter codes and orthographic loop for linking orthographic letter codes and finger sequencing codes), and Supervisory Attention (focused and switching attention and self-monitoring during written word finding). Multiple regressions showed that most predictors explained individual difference in at least one reading or writing outcome, but which predictors explained unique variance beyond shared variance depended on outcome. ANOVAs confirmed that research-supported criteria for dyslexia validated for younger children and their parents could be used to diagnose which adolescents and young adults did (n=31) or did not (n=50) meet research criteria for dyslexia. Findings are discussed in reference to the heterogeneity of phenotypes (behavioral markers of genetic variables) and their application to assessment for accommodations and ongoing instruction for adolescents and young adults with dyslexia.

Differential Diagnosis of Dysgraphia, Dyslexia, and OWL LD: Behavioral and Neuroimaging Evidence

In Study 1, children in grades 4 to 9 (N= 88, 29 females and 59 males) with persisting reading and/or writing disabilities, despite considerable prior specialized instruction in and out of school, were given an evidence-based comprehensive assessment battery at the university while parents completed questionnaires regarding past and current history of language learning and other difficulties. Profiles (patterns) of normed measures for different levels of oral and written language used to categorize participants into diagnostic groups for dysgraphia (impaired subword handwriting) (n=26), dyslexia (impaired word spelling and reading) (n=38), or oral and written language learning disability OWL LD (impaired oral and written syntax comprehension and expression) (n=13) or control oral and written language learners (OWLs) without SLDs (n=11) were consistent withreported history. Impairments in working memory components supporting language learning were also examined. In Study 2, right handed children from Study 1 who did not wear braces (controls, n=9, dysgraphia, n= 14; dyslexia, n=17, OWL LD, n=5) completed an fMRI functional connectivity brain imaging study in which they performed a word-specific spelling judgment task, which is related to both word reading and spelling, and may be impaired in dysgraphia, dyslexia, and OWL LD for different reasons. fMRI functional connectivity from 4 seed points in brain locations involved in written word processing to other brain regions also differentiated dysgraphia, dyslexia, and OWL LD; both specific regions to which connected and overall number of functional connections differed. Thus, results provide converging neurological and behavioral evidence, for dysgraphia, dyslexia, and OWL LD being different, diagnosable specific learning disabilities (SLDs) for persisting written language problems during middle childhood and early adolescence. Translation of the research findings into practice at policy and administrative levels and at local school levels is discussed.

Heritability, family, school and academic achievement in adolescence

We demonstrate how genetically informed designs can be applied to administrative exam data to study academic achievement. ACE mixture latent class models have been used with Year 6 and 9 exam data for seven cohorts of Polish students which include 24,285 pairs of twins. Depending on a learning domain and classroom environment history, from 58% to 88% of variance in exam results is attributable to heritability, up to 34% to shared environment and from 8% to 15% depends on unique events in students' lives. Moreover, between 54% and 66% of variance in students' learning gains made between Years 6 and 9 is explained by heritability. The unique environment accounts for between 34% and 46% of that variance. However, we find no classroom effects on student progress made between Years 6 and 9. We situate this finding against the view that classroom peer groups and teachers matter for adolescent learning.

Validity of large-scale reading tests: A phenotypic and behaviour-genetic analysis

Each year, all Australian students in grades 3, 5, 7, and 9 sit nationwide large-scale tests in literacy and numeracy, which have their validity frequently questioned. We compared the performance of Grade 3 twins on these large-scale reading tests with their performance on three individually administered literacy tests in comprehension, word reading and vocabulary within a genetically sensitive design. Comprehension, word reading, and vocabulary accounted for a substantial amount of the variance in school reading tests. Performance on large-scale reading tests and individually administered tests was moderately to substantially heritable and the same genes contributed to performance in both types of test. These results confirm that large-scale school reading tests measure, at least in part, the literacy skills tapped by individual tests that are frequently considered to be the "gold-standard" in testing.

Why do Children Differ in Their Development of Reading and Related Skills?

Modern behavior-genetic studies of twins in the U.S., Australia, Scandinavia, and the U.K. show that genes account for most of the variance in children's reading ability by the end of the first year of formal reading instruction. Strong genetic influence continues across the grades, though the relevant genes vary for reading words and comprehending text, and some of the genetic influence comes through a gene - environment correlation. Strong genetic influences do not diminish the importance of the environment for reading development in the population and for helping struggling readers, but they question setting the same minimal performance criterion for all children.

Predicting Levels of Reading and Writing Achievement in Typically Developing, English-Speaking 2nd and 5th Graders

Human traits tend to fall along normal distributions. The aim of this research was to evaluate an evidence-based conceptual framework for predicting expected individual differences in reading and writing achievement outcomes for typically developing readers and writers in early and middle childhood from Verbal Reasoning with or without Working Memory Components (phonological, orthographic, and morphological word storage and processing units, phonological and orthographic loops, and rapid switching attention for cross-code integration). Verbal Reasoning (reconceptualized as Bidirectional Cognitive-Linguistic Translation) plus the Working Memory Components (reconceptualized as a language learning system) accounted for more variance than Verbal Reasoning alone, except for handwriting for which Working Memory Components alone were better predictors. Which predictors explained unique variance varied within and across reading (oral real word and pseudoword accuracy and rate, reading comprehension) and writing (handwriting, spelling, composing) skills and grade levels (second and fifth) in this longitudinal study. Educational applications are illustrated and theoretical and practical significance discussed.

Strong genetic influence on a UK nationwide test of educational achievement at the end of compulsory education at age 16

We have previously shown that individual differences in educational achievement are highly heritable in the early and middle school years in the UK. The objective of the present study was to investigate whether similarly high heritability is found at the end of compulsory education (age 16) for the UK-wide examination, called the General Certificate of Secondary Education (GCSE). In a national twin sample of 11,117 16-year-olds, heritability was substantial for overall GCSE performance for compulsory core subjects (58%) as well as for each of them individually: English (52%), mathematics (55%) and science (58%). In contrast, the overall effects of shared environment, which includes all family and school influences shared by members of twin pairs growing up in the same family and attending the same school, accounts for about 36% of the variance of mean GCSE scores. The significance of these findings is that individual differences in educational achievement at the end of compulsory education are not primarily an index of the quality of teachers or schools: much more of the variance of GCSE scores can be attributed to genetics than to school or family environment. We suggest a model of education that recognizes the important role of genetics. Rather than a passive model of schooling as instruction (instruere, ‘to build in’), we propose an active model of education (educare, ‘to bring out’) in which children create their own educational experiences in part on the basis of their genetic propensities, which supports the trend towards personalized learning.

Expanding the environment: gene × school-level SES interaction on reading comprehension

BACKGROUND

Influential work has explored the role of family socioeconomic status (SES) as an environmental moderator of genetic and environmental influences on cognitive outcomes. This work has provided evidence that socioeconomic circumstances differentially impact the heritability of cognitive abilities, generally supporting the bioecological model in that genetic influences are greater at higher levels of family SES. The present work expanded consideration of the environment, using school-level SES as a moderator of reading comprehension.

METHODS

The sample included 577 pairs of twins from the Florida Twin Project on Reading, Behavior and Environment. Reading comprehension was measured by the Florida Comprehensive Achievement Test (FCAT) Reading in third or fourth grade. School-level SES was measured by the mean Free and Reduced Lunch Status (FRLS) of the schoolmates of the twins.

RESULTS

The best-fitting univariate G × E moderation model indicated greater genetic influences on reading comprehension when fewer schoolmates qualified for FRLS (i.e., 'higher' school-level SES). There was also an indication of moderation of the shared environment; there were greater shared environmental influences on reading comprehension at higher school-level SES.

CONCLUSIONS

The results supported the bioecological model; greater genetic variance was found in school environments in which student populations experienced less poverty. In general, 'higher' school-level SES allowed genetic and probably shared environmental variance to contribute as sources of individual differences in reading comprehension outcomes. Poverty suppresses these influences.

Literacy and numeracy are more heritable than intelligence in primary school

Because literacy and numeracy are the focus of teaching in schools, whereas general cognitive ability (g, intelligence) is not, it would be reasonable to expect that literacy and numeracy are less heritable than g. Here, we directly compare heritabilities of multiple measures of literacy, numeracy, and g in a United Kingdom sample of 7,500 pairs of twins assessed longitudinally at ages 7, 9, and 12. We show that differences between children are significantly and substantially more heritable for literacy and numeracy than for g at ages 7 and 9, but not 12. We suggest that the reason for this counterintuitive result is that universal education in the early school years reduces environmental disparities so that individual differences that remain are to a greater extent due to genetic differences. In contrast, the heritability of g increases during development as individuals select and create their own environments correlated with their genetic propensities.

Reading development in young children: genetic and environmental influences

The development of reading skills in typical students is commonly described as a rapid growth across early grades of active reading education, with a slowing down of growth as active instruction tapers. This study examined the extent to which genetics and environments influence these growth rates. Participants were 371 twin pairs, aged approximately 6 through 12, from the Western Reserve Reading Project. Development of word-level reading, reading comprehension, and rapid naming was examined using genetically sensitive latent quadratic growth curve modeling. Results confirmed the developmental trajectory described in the phenotypic literature. Furthermore, the same shared environmental influences were related to early reading skills and subsequent growth, but genetic influences on these factors were unique.

Reading development in young children: genetic and environmental influences

The development of reading skills in typical students is commonly described as a rapid growth across early grades of active reading education, with a slowing down of growth as active instruction tapers. This study examined the extent to which genetics and environments influence these growth rates. Participants were 371 twin pairs, aged approximately 6 through 12, from the Western Reserve Reading Project. Development of word-level reading, reading comprehension, and rapid naming was examined using genetically sensitive latent quadratic growth curve modeling. Results confirmed the developmental trajectory described in the phenotypic literature. Furthermore, the same shared environmental influences were related to early reading skills and subsequent growth, but genetic influences on these factors were unique.

A multivariate twin study of early literacy in Japanese Kana

This first Japanese twin study of early literacy development investigated the extent to which genetic and environmental factors influence individual differences in prereading skills in 238 pairs of twins at 42 months of age. Twin pairs were individually tested on measures of phonological awareness, kana letter name/sound knowledge, receptive vocabulary, visual perception, nonword repetition, and digit span. Results obtained from univariate behavioral-genetic analyses yielded little evidence for genetic influences, but substantial shared-environmental influences, for all measures. Phenotypic confirmatory factor analysis suggested three correlated factors: phonological awareness, letter name/sound knowledge, and general prereading skills. Multivariate behavioral genetic analyses confirmed relatively small genetic and substantial shared environmental influences on the factors. The correlations among the three factors were mostly attributable to shared environment. Thus, shared environmental influences play an important role in the early reading development of Japanese children.

Multivariate genetic analysis of learning and early reading development

The genetic factor structure of a range of learning measures was explored in twin children, recruited in preschool and followed to Grade 2 (total N = 2084). Measures of orthographic learning and word reading were included in the analyses to determine how these patterned with the learning processes. An exploratory factor analysis of the genetic correlations among the variables indicated a three-factor model. Vocabulary tests loaded on the first factor, the Grade 2 measures of word reading and orthographic learning, plus preschool letter knowledge, loaded on the second, and the third was characterized by tests of verbal short-term memory. The three genetic factors correlated, with the second (print) factor showing the most specificity. We conclude that genetically-influenced learning processes underlying print-speech integration, foreshadowed by preschool letter knowledge, have a degree of independence from genetic factors affecting spoken language. We also argue that the psychology and genetics of associative learning be afforded a more central place in studies of reading (dis)ability, and suggest some links to molecular studies of the genetics of learning.

Modeling the Etiology of Individual Differences in Early Reading Development: Evidence for Strong Genetic Influences

We explored the etiology of individual differences in reading development from post-kindergarten to post-4^th grade by analyzing data from 487 twin pairs tested in Colorado. Data from three reading measures and one spelling measure were fit to biometric latent growth curve models, allowing us to extend previous behavioral genetic studies of the etiology of early reading development at specific time points. We found primarily genetic influences on individual differences at post-1^st grade for all measures. Genetic influences on variance in growth rates were also found, with evidence of small, nonsignificant, shared environmental influences for two measures. We discuss our results, including their implications for educational policy.

The Russian School Twin Registry (RSTR): project PROGRESS

The Russian School Twin Registry (RSTR) was established in 2012, supported by a grant from the Government of the Russian Federation. The main aim of the registry is to contribute to Progress in Education through Gene-Environment Studies (PROGRESS). The formation of the registry is ongoing and it is expected that most schools in the Russian Federation (approximately 50,000 schools) will contribute data to the registry. With a total of 13.7 million students in Grades 1-11 (ages 7-18), the potential number of twin pairs exceeds 100,000. Apart from the large sample size and its representative nature, the RSTR has one unique feature: in collaboration with the International Advisory Committee to the Registry, genetically sensitive cross-cultural investigations are planned, aided by the use of the common assessment instruments. Other strengths of the registry include the assessment of a large sample of non-twin school children, including those studying in the same classes as the twins in the registry. It is hoped that the RSTR will provide an important research platform for national and international educationally relevant research.

Task avoidance, number skills and parental learning difficulties as predictors of poor response to instruction

Altogether 1,285 Finnish children were followed up from the end of kindergarten through Grade 1. All were nonreaders at school entrance. The aim was to delineate predictors of resistance to treatment that are evidenced as little or no reading progress during Grade 1. On the basis of reading achievement in Grade 1 spring, four subgroups were formed. These were fast, average, and slow reading acquisition and slow progress in both reading and math. Kindergarten spring scores in phonological awareness, letter knowledge, rapid naming, and number skills differentiated well among the groups, the latter two being more robust predictors. Task avoidance added to the prediction over and above cognitive skills. Its effect disappeared when parental history of reading and math difficulties was included in the equation. The present results depict poor response to instruction as a general learning problem rather than a specific reading difficulty. Poor response to instruction differs from dyslexia also in that treatment resisters start school with cognitive prerequisites that do not indicate severe reading and math problems.

Dynamic and static assessment of phonological awareness in preschool: a behavior-genetic study

The genetic and environmental overlap between static and dynamic measures of preschool phonological awareness (PA) and their relation to preschool letter knowledge (LK) and kindergarten reading were examined using monozygotic and dizygotic twin children (maximum N = 1,988). The static tests were those typically used to assess a child's current level of PA such as blending and elision, and the dynamic test included instruction in phoneme identity to assess the child's ability to respond to this instruction. Both forms were influenced by genes and by shared and nonshared environment. The static and dynamic versions were influenced by the same genes, and part of the total genetic influence was shared with LK. They were subject to both overlapping and independent shared environment influences, with the component in common also affecting LK. Nonshared environment influences were mostly independent. Scores from dynamic assessment added only minimally to variance explained in kindergarten reading after LK and static assessment had been factored in. Although one of the genetic factors that influenced both forms of PA also affected kindergarten reading, it was only the one shared with LK. The authors conclude that dynamic assessment of PA in preschool offers little advantage over the more commonly used static forms, especially if LK scores are available, although they acknowledge its potential in cases of preschool educational disadvantage.

Phonological Awareness and Rapid Automatized Naming Predicting Early Development in Reading and Spelling: Results from a Cross-Linguistic Longitudinal Study

In this study, the relationship between latent constructs of phonological awareness (PA) and rapid automatized naming (RAN) were investigated and related to later measures of reading and spelling in children learning to read in different alphabetic writing systems (i.e., Norwegian/Swedish vs. English). 750 U.S./Australian children and 230 Scandinavian children were followed longitudinally between kindergarten and 2nd grade. PA and RAN were measured in kindergarten and Grade 1, while word recognition, phonological decoding, and spelling were measured in kindergarten, Grade 1, and Grade 2. In general, high stability was observed for the various reading and spelling measures, such that little additional variance was left open for PA and RAN. However, results demonstrated that RAN was more related to reading than spelling across orthographies, with the opposite pattern shown for PA. In addition, tests of measurement invariance show that the factor loadings of each observed indicator on the latent PA factor was the same across U.S./Australia and Scandinavia. Similar findings were obtained for RAN. In general, tests of structural invariance show that models of early literacy development are highly transferable across languages.

Genetic and Environmental Influences on Vocabulary and Reading Development

Genetic and environmental relations between vocabulary and reading skills were explored longitudinally from preschool through grades 2 and 4. At preschool there were strong shared-environment and weak genetic influences on both vocabulary and print knowledge, but substantial differences in their source. Separation of etiology for vocabulary and reading continued for word recognition and decoding through grade 4, but genetic and environmental correlations between vocabulary and reading comprehension approached unity by grade 4, when vocabulary and word recognition accounted for all of the genetic and shared environment influences on reading comprehension.

Inter-relationships among behavioral markers, genes, brain and treatment in dyslexia and dysgraphia

Cross-country, longitudinal twin studies provide strong evidence for both the biological and environmental basis of dyslexia, and the stability of genetic influences on reading and spelling, even when skills improve in response to instruction. Although DNA studies aimed at identifying gene candidates in dyslexia and related phenotypes (behavioral expression of underlying genotypes); and imaging studies of brain differences between individuals with and without dyslexia and the brain's response to instructional treatment are increasing, this review illustrates, with the findings of one multidisciplinary research center, an emerging trend to investigate the inter-relationships among genetic, brain and instructional treatment findings in the same sample, which are interpreted in reference to a working-memory architecture, for dyslexia (impaired decoding and spelling) and/or dysgraphia (impaired handwriting). General principles for diagnosis and treatment, based on research with children who failed to respond to the regular instructional program, are summarized for children meeting research criteria for having or being at risk for dyslexia or dysgraphia. Research documenting earlier emerging specific oral language impairment during preschool years associated with reading and writing disabilities during school years is also reviewed. Recent seminal advances and projected future trends are discussed for linking brain endophenotypes and gene candidates, identifying transchromosomal interactions, and exploring epigenetics (chemic al modifications of gene expression in response to developmental or environmental changes). Rather than providing final answers, this review highlights past, current and emerging issues in dyslexia research and practice.

Genetic and Environmental Influences on Inattention, Hyperactivity-Impulsivity, and Reading: Kindergarten to Grade 2

Twin children from Australia, Scandinavia and the USA were assessed for inattention, hyperactivity-impulsivity and reading across the first three school years. Univariate behavior-genetic analyses indicated substantial heritability for all three variables in all years. Longitudinal analyses showed one genetic source operating across the time span and a second entering in the second school year for each variable, though possibly not reliable for inattention. Other analyses confirmed previous findings of pleiotropy (shared genes) between inattention and reading, and showed that this genetic overlap is in place from kindergarten onwards and is restricted to one of the genetic sources that affect reading and inattention. The results extend previous conclusions about the developmental trajectories of inattention, hyperactivity-impulsivity, and reading and their relationships. Limitations of this studyare discussed, as are educational implications.

Genetic influence on literacy constructs in kindergarten and first grade: evidence from a diverse twin sample

Historically, twin research on reading has been conducted on older children and the generalizability of results across racial/ethnic/socioeconomic groups is unclear. To address these gaps, early literacy skills were examined among 1,401 twin pairs in kindergarten and 1,285 twin pairs in first grade (ages 5-7). A multi-group analysis was conducted separately for subsamples defined by neighborhood income while controlling for race/ethnicity within each grade. Substantial additive genetic and shared environmental effects were found for early literacy skills measured in kindergarten. In first grade, variance in early reading was associated with large additive genetic effects for middle and high neighborhood income twins, but shared environmental influence was substantial for low neighborhood income twins. Results suggest that the etiological architecture of some early literacy skills may differ across economic contexts.

Genetic and environmental influences on the growth of early reading skills

BACKGROUND

Studies have suggested genetic and environmental influences on overall level of early reading whereas the larger reading literature has shown environmental influences on the rate of growth of early reading skills. This study is the first to examine the genetic and environmental influences on both initial level of performance and rate of subsequent growth in early reading.

METHODS

Participants were drawn from the Western Reserve Reading Project, a study of 314 twin pairs based in Ohio. Twins were assessed via three annual home visits during early elementary school. Assessments included word identification, letter identification, pseudoword decoding, expressive vocabulary, phoneme awareness, and rapid naming. Measures were analyzed using latent growth curve modeling.

RESULTS

The heritability of initial performance (latent intercept) ranged from h(2) = .38 for word identification to h(2) = .72 for rapid naming. Shared environment ranged from c(2) = .11 for rapid naming to c(2) = .62 for word identification. The heritability of the rate of subsequent growth (latent slope) was statistically significant for rapid naming h(2) = .58 and phoneme awareness h(2) = .20. Shared environment accounted for nearly 100% of variance in rate of growth for word identification, letter identification and pseudoword decoding, and was statistically significant and large for phoneme awareness (c(2) = .80). Genetic variance for rapid naming and phoneme awareness latent slopes overlapped entirely with genetic variance on the intercepts. In contrast, one-third to two-thirds of the shared environmental variance on the slope was independent from the shared environmental variance on the intercept.

CONCLUSIONS

Genetic influences were related primarily to those already present at the initial level of performance. In contrast, shared environmental influences affecting rate of growth were both predicted by and independent from initial levels of performance. Results suggested that growth in early reading skills is amenable to family, school, or other environmental influences as reading skills develop.

Predicting reading and spelling difficulties in transparent and opaque orthographies: a comparison between Scandinavian and US/Australian children

In this study, predictors of reading and spelling difficulties among children learning more transparent (Norwegian/Swedish) and less transparent (English) orthographies were examined longitudinally from preschool through Grade 2 using parallel versions of tests. A series of logistic regression analysis indicated three main findings. First, phonological awareness as a predictor of reading difficulties in the Scandinavian sample was time-limited to Grade 1, but remained as a significant predictor in the English-speaking sample. Second, phonological awareness predicted spelling difficulties similarly across orthographies. Third, preschool and kindergarten RAN was a significant predictor of reading and spelling difficulties at both Grades 1 and 2 across orthographies. The authors conclude that phonological awareness diminishes as a predictor of reading difficulties in transparent orthographies after the first years of schooling, that RAN is a better long-term predictor of reading difficulties, and that phonological awareness is associated with spelling difficulties similarly in transparent and opaque orthographies.

"Teacher Effects" in Early Literacy Development: Evidence from a Study of Twins

It is often assumed that differences in teacher characteristics are a major source of variability in children's educational achievements. We examine this assumption for early literacy achievement by calculating the correlations between pairs of twin children who either share or do not share a teacher in kindergarten, Grade 1, and Grade 2. Teacher effects, or more strictly classroom effects, would show up as higher correlations for same- than different-class twin pairs. Same-class correlations were generally higher than different-class correlations, though not significantly so on most occasions. On the basis of the results we estimate that the maximum variance accounted for by being assigned to same or different classrooms is 8%. This is an upper-bound figure for a teacher effect because factors other than teachers may contribute to variation attributable to classroom assignment. We discuss the limitations of the study and draw out some of its educational implications.