The overall purpose of the national Head Start evaluation is to assess the impact, on the children and parents being served, of: (1) the educational services component of Head Start, and (2) a new demonstration program within Head Start, Basic Educational Skills. The evaluation deals with a total of 65 Head Start programs and their families. This longitudinal study will focus on the preschool and elementary experiences of three groups: those in typical Head Start programs, those who are eligible but not enrolled in Head Start, and those who participate in the Basic Educational Skills program. The dominant issue is the relationship between program delivery and program effects on a national scale. Site visits to selected Head Start programs were conducted in spring, 1979. The results of these site visits are reported in terms of determinants of implementation, characteristics of the program and its context, implementation/process variables, curriculum resources, parent involvement, continuity, and opportunity to benefit. Future phases of the evaluation are described. (BW)