This report summarizes the findings of previous technical reports on the immediate changes in child development associated with Head Start and presents a statement of the extent to which these changes have been enhanced or attenuated by different program experiences for different children. Background information presented includes an overview of the findings; a history of Project Head Start; and an overview of Head Start Evaluations (descriptive studies, on-site research and evaluation studies, national impact studies, national interaction model studies). A section devoted to design and measurement examines methodological issues, design issues, data collection, measures, and statistical analytic models. A section on findings covers questions concerned with characteristics of Head Start children and families, effectiveness of Head Start programs and teacher approaches, and children's performance gains. A discussion section examines factors influencing developmental changes and implications for early childhood intervention. Appendices are (1) Measure Selection and Psychometric Characteristics and (2) Selection of Variables for Analysis. (JH)