Of primary interest in this study was the effect of general ability on learning. It was hypothesized that students higher in general ability would obtain higher posttest scores on the average than lower ability students, and that verbal and figural explanatory supplements to minimal instructional materials would reduce the regression of general ability on outcome. It was expected that students with higher aptitude scores would obtain higher posttest scores. The effects of a more task-specific aptitude, graph processing, were explored, and involved both immediate and delayed learning outcome measures. A course in Economics was presented to high-school students using one of three sets of instructional materials. Before the course, participants took a three-hour aptitude battery and were randomly assigned to treatment. Posttests were administered at the end of the course and two weeks later. Generalized regression analysis was used to assess the effects of aptitudes, treatments, and interactions. This study provided evidence that neither aptitude nor instructional treatment alone can fully describe learning outcomes. Further, instructional supplements, can be effective in filling in for student weaknesses and reducing differences between high and low ability students. (Author/GK)