An attempt is made to show generally that variations in aggregate intelligence scores are closely associated with variations in patterns of family configuration and that these aggregate family factors are deeply implicated in the declining Scholastic Aptitude Test (SAT) scores the discussion summarizes a recent theoretical analysis that specifies the conditions under which family configuration may foster or impede intellectual growth and examines some relevant empirical findings finally returning to the special case of the SATs. A variety of findings reveal the impact of family configuration on intelligence: intellectual performance increases with decreasing family size; children born early in the sibship perform births are relatively short; long intersibling spacing appears to cancel the negative effects of birth order and in extreme cases to reverse them; in general long intervals enhance intellectual growth; the adverse effects of short intervals are reflected in the typically low intelligence quotients (IQs) of children of multiple births; only children the benefits of a small family are apparently counteracted by the lack of opportunities to serve as teachers to younger children; last children suffer that handicap also; temporal changes in family patterns such as birthrates average orders of births intervals between children and family size are reflected in temporal changes in aggregate measures of intellectual performance; and males and females differ in average birth order and this difference is reflected in aggregate intellectual performance scores. The pattern of these diverse data is consistent with the analysis of intellectual development based on the confluence model. Not all variation in intelligence is accounted for by variation in family configuration. For example the large decline in SAT Scores in the US cannot be a function of changes in family configuration alone because it is considerably larger that would be expected on the basis of a simple extrapolation from the four national samples.
Robert B. Zajonc (Fri,) studied this question.