This monograph presents a longitudinal investigation of child development and family well-being during the first decade of life for children with Down syndrome, motor impairment, or developmental delay of uncertain etiology. It was found that, although the child's type of disability predicts some features of development, the child's motivation and the quality of relationships established between mothers and children and among family members are consistent predictors of the development of cognitive, social, communication, and daily living skills. Further, both mothers and fathers report increasing levels of stress as their children grow older. The child's behavior problems are a consistent predictor of these increases, but the parents' abilities to problem-solve and garner support are ameliorating factors. The findings suggest two general conclusions. First changes in selected policies and practices can improve outcomes for children with disabilities and their parents. Second, the study of children with developmental disabilities and their families can enhance the overall science of child development.