A correspondence exists between a simplified data collection method employing results from a post test for graphic skills in kinematics, and a rigourous validation method. Examination of test responses for discrepant instances yielded further information of value. Hierarchical patterns of learning and remembering are identical. (Author/CP)

As an example, two aspects of children's conservation are explained: decalages and the shift from perceptual to quantitative cues. This approach, relative to structuralist formulation, involves cognitive factors such as prior learning, as well as impinging social experience. It is compatible with Piaget's theory, yet simpler and more flexible. (CP)