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.

Numerous twin studies have been published examining the genetic and environmental etiology of reading comprehension, though the etiological estimates may be influenced currently unidentified sample conditions (e.g., Tucker-Drob & Bates, 2015). The purpose of the current meta-analysis was to average the etiological influences of reading comprehension and to explore the potential moderators that may be influencing these estimates. Results revealed an average heritability estimate of h2 = .59, with significant variation in estimates across studies, suggesting potential moderation. Heritability was moderated by publication year, grade level, project, zygosity determination method, and response type. The average shared environmental estimate was c2 = .16, with publication year, grade and zygosity determination method acting as significant moderators. These findings support the large role of genetic influences on reading comprehension, and a small but significant role of shared environmental influences. The significant moderators of etiological influences within the current synthesis suggest our interpretation of how genes and environment influence reading comprehension should reflect aspects of study and sample.

Gene–environment processes tell us how genetic predispositions and environments work together to influence children in schools. One type of gene–environment process that has been extensively studied using behavioral genetics methods is a gene‐by‐environment interaction. A gene‐by‐environment interaction shows us when the effect of your context on a phenotype differs depending on your genetic predispositions, or vice versa, when the effect of your genetic predispositions on a phenotype differs depending on your context. Developmental behavioral geneticists interested in children's school achievement have examined many different contexts within the gene‐by‐environment interaction model, including contexts measured from within children's home and school environments. However, this work has been overwhelmingly focused on WEIRD samples children, leaving us with non‐inclusive scientific evidence. This can lead to detrimental outcomes when we overgeneralize this non‐inclusive scientific evidence to racialized groups. We conclude with a call to include racialized children in more research samples.

Recent research suggests that the etiology of reading achievement can differ across environmental contexts. In the US, schools are commonly assigned grades (e.g., “A,” “B”) often interpreted to indicate school quality. This study explored differences in the etiology of early literacy skills for students based on these school grades. Participants included twins drawn from the Florida Twin Project on Reading (n=1313 pairs) aged 4 to 10 years during the 2006–2007 school year. Early literacy skills were assessed with DIBELS subtests: Oral Reading Fluency (ORF), Nonsense Word Fluency (NWF), Initial Sound Fluency (ISF), Letter Naming Fluency (LNF), and Phoneme Segmentation Fluency (PSF). School grade data was retrieved from the Florida Department of Education. Multi-group analyses were conducted separately for subsamples defined by “A” or “non-A” schools, controlling for school-level socioeconomic status. Results indicated significant etiological differences on pre-reading skills (ISF, LNF, and PSF), but not word-level reading skills (ORF and NWF). There was a consistent trend of greater environmental influences on pre-reading skills in non-A schools, arguably representing “poorer” environmental contexts than the A-schools. Importantly, this is the case outside of resources linked with school-level SES, indicating that something about the direct environment on pre-reading skills in the non-A-school context is more variable than for A-schools.

According to the Hybrid Model (van Bergen et al., 2014), the significant association among Executive functioning (EF), reading, and math may be partially explained by parent-reported EF's role as a common risk and/or protective factor in reading and math (dis)abilities. The current study used a sample of 434 twin pairs (Mage = 12.12) from Florida to conduct geneticallysensitive modeling on children's parent-reported EF, reading, and math skills to determine the common and unique etiological influences among the three domains. EF was measured through parent report and reading and math were measured with standardized test scores drawn from Florida's Progress Monitoring and Reporting Network as well as standardized parentadministered assessments collected by mail. Our trivariate Cholesky modeling showed that no matter which parent-reported EF component was modeled, the overlap of parent-reported EF with reading and math was explained by common genetic influences. Supplemental analysis suggested that this might in part be due to general parent report of problem behaviors. Additionally, significant environmental influences, with higher shared environmental overlap than previous work, were also found for reading and math. Findings indicate that poor parentreported EF is a common cognitive risk factor for reading and math disabilities, which is driven by a shared genetic basis among all three domains.