Supporting earlier research evidence showing that participation in school activities is related to later positive cognitive, social, and personality development, the findings of this study suggest that the advantages for the well rounded development of the individual student in small schools--those graduating 150 or fewer students per year--may have been overlooked in the rush to put large numbers of students together in ever larger high schools. The study surveyed 1982 and 1983 yearbook lists of activities of almost 9,000 seniors from 24 central New York state public high schools with senior classes ranging from 21 to 622 students. Findings show that while larger schools offer more activities, smaller schools have higher rates of student participation for both sexes. Especially noteworthy are the much higher percentages of students from larger schools relative to students from small schools showing no participation whatever in any of the school's activities. Evidence indicates that the small schools with their relatively underpopulated settings encourage participation by many students; the students themselves can see they are needed for successful operation of the setting. (NEC)