Growth in reading and math ability: A behavioral genetic analysis

Background: Research shows that mathematics and reading abilities are associated, and while there is evidence showing that individual differences in reading growth are due to environmental influences, this is the first study to examine the genetic and environmental influences on the growth of math ability, and whether or not they are similar to growth in reading ability. Methods: Participants were drawn from the Western Reserve Reading and Math Project, a study of 314 twin pairs based in Ohio. Twins were assessed at three annual home visits at approximately ages 10, 11, and 12. Assessments included two measures of mathematics performance from the Woodcock Johnson Tests of Achievement III: Calculation and Fluency. Measures were analyzed using a quantitative genetic latent growth curve model. Results: Just as was found for growth in reading ability, genetic and shared environmental influences were significant on initial performance (latent intercept) for all three math measures. Shared environmental influences on growth were significant for Fluency and Calculation, while there was no significant influence attributable to genetics. Finally, none of the observed outcomes showed significant genetic or environmental overlap between the intercept and slope. Conclusions: Genetic influences are important for initial performance, but are not related to growth in mathematics performance. The significant growth observed for Calculation was due to environmental influences. This matches exactly with what was found for reading growth, implying that the two abilities may share influences and should be further studied as such.