Little is known about the etiology of individual differences in psychological development during middle childhood, an era marked by changes in cognitive and social behavior nearly as dramatic as those seen during the transition from infancy to early childhood or during adolescence. The proposed research will apply the most powerful quantitative (biometrical) genetic methodology, the "full" adoption design in which data are collected from both birth and adoptive parents, to the study of psychological development in 7-year-olds. The sample is unique: over 400 adopted and matched nonadopted children who previously have been studied in their homes at 1, 2, 3, and 4 years of age using an extensive set of psychological and environmental assessments. The birth parents and adoptive parents of the adoptees and the parents of the nonadopted children have been administered a 3-hour battery of psychological measures. The proposed 5-year project will provide for testing the 7-year-old adopted and nonadopted children on a multidimensional battery of psychological measures including general and specific cognitive abilities, communicative skills, school achievement, temperament, behavioral problems, motoric development, and social interaction. The project will capitalize on the potent design and the extensive data set previously collected as part of the Colorado Adoption Project in applying multivariate, longitudinal, and quatitative genetic analyses to data obtained during the important developmental period marked by the beginning of formal schooling. The results of these analyses, which will substantially advance our understanding of the etiology of individual differences in functioning during this critical epoch, are likely to have important implications for childrearing, education, and mental health.