This study examined the effects of family size on a sample of some 5000 students in Bayamon, Puerto Rico and examined the effects of family size and spacing on some 537 families in four suburban towns near Boston. It was found that there were major effects of both socio-economic status and religion on family size, but that the direction of the effect was opposite in the two samples. In the U.S. higher status families tended to have more children than their counterparts in Puerto Rico. In the U.S. non-Catholics tended to have smaller families than the Catholics, while in Puerto Rico the non-Catholics had the larger families. Both in Puerto Rico and the U.S. small family mothers were more likely to have worked both prior to and after marriage than large family mothers. In both cultures small family children felt more accepted by their parents. Generally, small family children in both cultures were more intelligent and did better in school than did large family children. American children distantly spaced from the next youngest child were more oriented toward college. When two children were closely spaced, the older was more authoritarian and the younger was more obedient, serious, emotionally stable, and careless of protocol. Both younger and older siblings were less intelligent if they were closely spaced. (Author/JM)