Determines patterns of differential human development in a longitudinal study of 417 male and 358 female college students ages 18 to 30. Findings suggest individuality in development is associated with significant qualitative individual differences that are best described on a cross-time basis. (BJD)

Outlines Piaget's late ideas on categories and morphisms and the impact of these ideas on the comprehension of the inclusion relationship and the solution of arithmetic problems. Reports a study in which fourth through sixth graders were given arithmetic problems involving two known quantities associated with changes rather than states. Identified…