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 report describes the activities directly relevant to the child test data, including the development of the test battery and the data collection procedures, and presents analyses of those data. The process for selection of the child measures for the fall 1979 data collection is summarized. The procedures used for the assignment of children to groups and the collection of child descriptive and test data are described. The children in the first cohort are described in terms of background and test information. The random assignment process is reviewed and the psychometric properties of the child measures are described. Appendix A contains a copy of the child testing booklet. (Author/BW)