The purpose and design of a longitudinal study of Project Head Start is summarized in this document, the fourth in a set of ten reports documenting the project. (Material from Project Report 3 was used extensively in preparing this document.) The study was designed to evaluate on a nationwide basis the Head Start Educational Services and to evaluate the Basic Educational Skills Program (BES), a recent demonstration project of Head Start. The intent of the longitudinal study was to follow children and their parents from preschool through fourth grade. The major evaluation topics addressed in the study included the following: the types of educational approaches used to teach Head Start participants (these approaches were compared to approaches used in alternative service settings); the effects of different intervention approaches on outcomes for Head Start participants; and a comparative analysis of Head Start participants in BES and Head Start participants not in BES. The dominant issues contained in this set of evaluation topics focused on the relationships between program delivery and child outcomes, including cognitive, communication and social skills. Cognitive and communication skills were measured by a battery of standardized tests, teacher reports, and observational techniques. Social skills were measured by a standardized test. The tests and how they were selected are identified. (Author/DB)