This study focuses on the effects of family size and spacing on intellectual, social, and personality development of children. The sample consisted of 533 suburban, middle class, large family (five or more) and small two child family children. The children, 233 boys and 300 girls, were teenagers attending either junior or senior high school. Spacing was measured as spacing to the next oldest and spacing to the next youngest. Spacing measures were divided into three categories: close (18 months or less); medium (19 to 30 months); and distant (more than 30 months). Standardized intelligence scores, the Test of Effective Academic Motivation, the Cattell High School Personality Questionnaire, questions about their participation in clubs, level of occupational aspiration, job orientation, and other personality scales were used. Conclusions show that the more closely spaced younger child was found to be less intelligent. However, these closely spaced children were also found to belong to more athletic teams, to be more interested in getting a job, to be more ambitious occupationally, to be more self-sufficient, more serious, and more relaxed about protocol. Most of these findings were significant only for large family children, spacing having less effect in children from two child families. (Author/JK)