Charting the Shift: Age as a Moderator of the Genetic and Environmental Influences on Reading

<p>Purpose: Reading skill is influenced by genes and environments throughout life. This study focused on the changes in heritability and environmental influences across the early to middle years of reading development. Reading theory suggests there is a shift from learning to read to reading to learn at approximately age 8. Based on the bioecological theory and gene-environment-time framework, as environmental influences stabilize we expected shared environmental influences to decrease and genetic influences to increase. Methods: Using a twin sample in the USA (N = 1086 individuals; 564 Male: 522 Female; Age M = 7.46 years, SD = 1.57, with 90% of families self-reported as White, 8% Black, 1% Asian, 1% Alaskan, Native American, or Native Pacific Islander, and 11% self-reported as Hispanic), we used a Gene-by-Environment (GxE) twin model with age as a moderator to examine how the balance of genetic and environmental influences on reading skill differed by age. Reading skill was measured with the DIBELS Next Composite from the beginning of academic year 2018/19. We estimated assessment age assuming the same fall test date for all participants. Results: We observed small increasing genetic influences and larger decreasing shared environmental influences on reading skill from ages 5 to 7 that began to plateau at approximately age 8. Non-shared environmental influences on reading skill were low and relatively stable from ages 6 through 12 following an uptick between ages 5 and 6. Conclusion: Results are consistent with the bioecological framework and the emerging gene-environment-time model. There were changes in the genetic and environmental influences on reading around the time that children began formal school-based instruction that began to level off during the shift from learning to read to reading to learn. Future work should identify specific environmental factors at these developmental windows to guide reading policies.</p>