Proposes a theoretical model of cognitive development and applies this model to the secondary analysis of two large-scale studies which focus on the acquisition of formal operational schemata by adolescents in the United States and Israel. Results support the "unity" hypothesis of cognitive development that the various schemata of formal…

Examines 11 elementary science texts in terms of conceptual structure and reasoning demands using concept maps. Reports that (1) the conceptual structures vary widely across texts; (2) most of the structures are well defined; and (3) the reasoning demands are above the developmental capabilities of most of primary-level children. (Author/YP)