Individual differences in general intelligence and in 8 different special aptitudes or skills were hypothesized to be independent of family size and birth order indices. Evidence to the contrary, in the form of linear correlations, was predicted to be due to the confounding influence of socio-economic factors. Among the more familiar demographic…

Research on sibling influence on intellectual ability has shown that academic ability and achievement decrease as family size increases and as spacing between siblings decreases. Research also suggests a relationship between sex of subject and of sibling, and age differences in the effects of birth order and sibling sex. (JAC)

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.…