This is the report of a study designed to test a model for determining the effectiveness of sets of instructional materials which can be considered hierarchical and to derive a mathematical relationship by which such measures can be quantified. The model tested requires that the instructional materials be hierarchical in character. The Introductory Physical Science (IPS) course was used in the study. The public schools in a suburban county provided the instructional setting. The model for measuring effectiveness proved, within the constraints of the study, to be a valid one when applied to the performance of boys in the IPS course. It worked especially well for boys of high ability. The model was not applicable in the case of girls' performance in the IPS course. The report also contains the investigator's evaluation of the IPS course and materials, some of the evaluation instruments used, and a bibliography. (LC)