Cites research findings to refute Piaget's contention of stages of cognitive development. Advocates continuous cognitive differentiation as a model. (CP)

Describes grade 9 student responses to instructional materials constructed on objectives derived from Piaget's balance and inclined place problems. Concludes the presence of a hierarchy only in the balance objectives. Indicates implications worthy of further studies. (CC)

Defines five levels between concrete and formal operation in the development of the concept of controlling variables. The sample, methodology and research on which the work is based is described in SE 519 500. (CP)