This is the third in a sequence of three papers describing an investigation of fifth graders' ability to learn to distinguish between valid and fallacious inferences from simple conditional premises. This paper presents the research design and results. (MN)

This study considers two problems related to cognitive development: "Is development hierarchical?" and "If so, what are the mechanisms involved in the process of development?" Analysis of the results of an experiment lead to differentiation of stages of development, and problem-solving strategies at each level are discussed.…

Some potential difficulties involved in using "real-life situations" in teaching problem solving are illustrated with a racing car problem. The importance of developing mental images and the ability to abstract in the solution process is indicated. (MP)