There is general agreement that intervention in the preschool years can reduce the long-term disability of children with pervasive developmental disorders (PDD), but the required components and optimal intensity of these programs remain unclear and recommended behavioral and educational treatments are not available in all communities. Moreover, preschool interventions often focus only on the child, leaving parents to manage the child's behavior on their own. Thus, although the role of parents as partners in the treatment team is universally acknowledged, few studies have tested parent-based interventions and large-scale interventions are non-existent. This project includes a five-site study to compare parent training to psychoeducation in 180 preschool-age children with PDD. Eligible subjects will be randomly assigned to receive either Parent Training (PT) or Psychoeducational Intervention (PEP) over 6 months. The primary outcomes are the change in the child's irritable and noncompliant behavior rated by the parent. Overall improvement and gains in adaptive functioning (social, communication, and daily living skill domains) will be assessed by a rater who is blind to treatment assignment. Parent-child interaction will be assessed in a semi-structured lab sequence by blinded raters. The effects of PT on parental stress and the possible moderating effects of concurrent interventions will also be explored. This trial is designed to provide information on optimal practices for educating parents to be effective teachers and advocates for their young children.