Introduces the confluence model as a theory specifying the process by which the intellectual environment modifies intellectual development. Using this model, explores the contradiction between prediction of secular trends in test scores by trends in aggregate birth order and the lack of prediction of individual test scores by birth order using…

Disparities between European countries and the U.S. in terms of incidence and prevalence of mild mental retardation have become apparent. A model of intellectual performance that might explain disparities and predict future levels of occurrence of mild mental retardation is presented. Such explanations are relevant for theory and policy decisions.…