In this study, a group of first graders who had attended full-year Head Start were compared cognitively to a group of first graders who had been eligible for Head Start but did not attend. Results of the study may be suspect because the children who participated in Head Start were selected from the most deprived of those eligible; therefore study groups may not have been comparable. Both groups were tested on the Stanford-Binet and the Preschool Inventory before and after first grade and on the Gates-MacGinitie Reading Test, Primary A, after first grade. Results indicated that at the beginning of the year the groups were the same in some areas and different in others. At the end of the first grade there were no significant differences between the two groups. The experimental group seemed to have a higher rate of gain than the control, but the difference was seldom significant. It is concluded that there is a tenuous case for saying that the similar scores of the two groups upon completion of first grade indicate the academic effectiveness of Head Start because the selection process placed the more deprived children in the experimental group. (MH)