This commentary on a paper by Douglas Detterman and others (EC 604 995), which tested a model assessing basic cognitive abilities in young adults with and without mental retardation, criticizes the paper for drawing conclusions not justified by the empirical results. (JDD)

This article finds the empirical review of the intellectual effects of family factors by Lala Carr Steelman wanting because (1) it is selective and incomplete; (2) it ignores systematic aggregate effects; (3) it imposes linear analysis on nonmonotone relationships; and (4) it disregards most of the confounds identified by Steelman as crucial.…

The author responds to criticism by R. B. Zajonc on a review of the extant literature on the intellectual consequences of sibship size and birth order. (Author/LMO)

Mathematics achievement differences among sixth-graders were analyzed in a four-wave design and explained by aptitude and instructional variables in a structural equation framework. The results demonstrate the local nature of achievement models in that neither their measurement nor structural components proved generalizable across two groups of…