Understanding the genetic and environmental mechanisms that underlie the development of reading ability and disability has important implications for literacy education and the prevention of learning disabilities in reading. To that end, the goal of the proposed competing continuation of HD38075 is to conduct a systematic developmental genetic examination of reading comprehension. The Western Reserve Reading Project includes a representative sample of 350 same-sex twin pairs born between 1996 and 1998 who, by the proposed start date, will have been assessed longitudinally across four measurement occasions from kindergarten through third grade on a broad battery of measures of reading skills, oral language skills, cognitive skills, mathematics, and family environmental factors. The proposed continuation will extend testing via three additional annual home visits spanning middle childhood to early adolescence, with a focus on emerging reading comprehension skills. We propose to examine the univariate genetic and environmental influences upon reading comprehension, the covariance between reading comprehension and oral language skills, decoding skills, and other related skills, as well as the relationship between proximal and distal measures of the home and school environments that are associated with reading comprehension and related skills. In doing so, the proposed research will offer a unique opportunity to examine the genetic and environmental etiology of the longitudinal development of reading comprehension and related skills during the critical transition from when children are "learning to read" to when they are "reading to learn." Extending the unique resources of the Western Reserve Reading Project is an important opportunity for a highly cost-effective and powerful genetically-sensitive investigation of the etiology of reading ability within its various developmental, cognitive, behavioral, and environmental contexts. Developing a more informative model of how genes and environments work together to affect the development of reading comprehension has important implications fostering reading development as well as to detect, ameliorate and prevent reading problems.