This preliminary report is the fourth in a series describing the progress of a 6-year longitudinal study by the Educational Testing Service (ETS). The present report specifically describes initial differences between children who go on to Head Start, and those who do not, based on results of 16 of the 33 measures administered in Year 1 (1969) in three of the study sites: Portland, Oregon; St. Louis, Missouri; and Trenton, New Jersey. In addition to test scores, information was collected on family and health. Comparisons are made in relation to the children themselves (sex, age, race, month of testing, test scores, and health information) and to their family situations. The results of the comparisons are discussed in relation to (a) relevant additional information on characteristics of Head Start population provided by the Office of Child Development/Head Start; and (b) related findings in the literature on disadvantaged children, especially in respect to Head Start attendance or non-attendance. Variables relating to the parental decision to send a child to Head Start are: Head Start attendance by an older sibling, the mother's employment status, the educational level of the parents, parental attitudes towards jobs and education, size of the family, race, and the child's sex. Other parts of the longitudinal study can be located as ED 037 486, ED 043 391, and ED 043 397. (Author/AJ)