Stability of genetic and environmental influences on reading performance at 7 and 12 years of age in the Colorado Adoption Project

Results obtained from longitudinal studies suggest that individual differen ces in reading performance are relatively stable over time. However, the ae tiology of this stability has not been previously explored. In the current study, the aetiology of longitudinal stability of reading performance betwe en 7 and 12 years of age was assessed using data from adoptive (97 unrelate d sibling pairs at age 7 and 73 pairs at age 12) and nonadoptive (106 relat ed pairs at age 7 and 75 pairs at age 12) children tested in the Colorado A doption Project. Results of a bivariate behavioural genetic analysis confir med earlier findings of moderate genetic influence on individual difference s in reading performance at both 7 and 12 years of age (h(2) = .49 and .37, respectively). Moreover, about 70% of the observed stability (r = .61) bet ween the two ages was due to common genetic influences. Of special interest , no new heritable or shared environmental variation was manifested at age 12, suggesting that the same genetic and shared environmental influences we re operating at both ages. In contrast, nonshared environmental influences (e.g. instructional methods, teachers, peers, etc.) were responsible for ch ange between 7 and 12 years of age, indicating the salience of such factors for the development of reading performance between middle childhood and ad olescence.