The construction and validation of a learning hierarchy designed to assist instruction in the skills of science hypothesis formation and testing are described. Results of the validation using prospective elementary teachers are described, and the revised hierarchy is presented. Revalidation results for a different group of teacher trainees are reported, and measures used to control pre-test effects during the validation procedures explained. Explanations for the lack of improvement in the skills following an eight-hour instructional sequence are given. (Arthor/AL)