Written for a variety of audiences, this volume describes the University of Western Ontario Preschool Project in sufficient detail to permit its replication; findings of formative and summative program evaluations are reported along with research developing new criterion measures of social competence. Begun in 1973, the program was primarily designed to meet the needs of economically disadvantaged preschool-age children in Canada. For comparative purposes, high income/high ability and low income/average ability groups attended the preschool. The children were tested for growth on intellectual and cognitive abilities, problem-solving styles and strategies, and social competence. Findings revealed that all three ability groups made significant gains over time on all measures. Chapter 1 of the present volume provides background information about intervention and research programs. Chapters 2 through 5 provide curriculum materials in the areas of number, classification, and spatial relations. Chapter 6 describes program modifications and special studies conducted in the third and fourth project years. Chapter 7 describes the development of a measure of social competence. Chapters 8 through 11 describe methods and discuss results of the summative evaluation of immediate and long term program impacts. Chapter 12 presents a summary and conclusions. Completing the document is an epilogue viewing the project and related issues from an updated (1983) perspective and exploring implications for social policy. (RH)