Intelligence and Family Size, 1949–1965

S ummary . An age‐group of 2,868 Aberdeen school children has been tested at ages 7, 9, 11 and 12, on verbal reasoning, non‐verbal reasoning and attainment tests. The relations between family size and test score were expressed as regression coefficients. The usual inverse relationship between family size and test score was observed. Regression coefficients from the verbal tests were larger than from the non‐verbal. Consistently larger regression coefficients were obtained for girls than for boys. Within social classes I and II, regression coefficients were smaller than within the other social classes. The results are interpreted as evidence of environmental influence on test scores. Results obtained from previous investigations in Aberdeen are compared with those obtained in the present study.