Critiques Rodgers et al.'s June 2000 research on the relation between birth order and intelligence, which suggests that it is a methodological illusion. Explains how the intellectual environment and the teaching function (whereby older children tutor younger ones) contribute to the growth of intellectual maturity, the first negatively and the…

A confluence model is developed that explains the effects of birth order and family size on intelligence. (Editor)

Theoretical predictions, based on the confluence model, were made for data from six national surveys of intellectual performance, each relating intellectual performance scores to family configuration variables. The confluence model was capable of accurate prediction in all cases when three parameters were estimated. (Author/RD)

Discusses the controversy of the relationship between birth order and intellectual performance through a detailed evaluation of the confluence model which assumes that the rate of intellectual growth is a function of the intellectual environment within the family and associated with the special circumstances of last children. (CM)

The confluence model shows the influence of family on intellectual growth. The decline of SAT scores is related to changing family patterns. Intellectual growth is lower for children with many siblings. The increase in average family size for the cohorts taking SATs between 1963 and 1980 caused scores to decline. (Author/VM)

Birth order effects on intellectual performance show both positive and negative results. Considers the intellectual aspects of siblings' changing environments, explaining that birth order and family size effects depend crucially on the age at which children are tested. Within-family data conceal patterns of aggregate effects that are revealed by…