Theory-based prototype computer-video instructional modules were developed to serve as an instructional supplement for students experiencing difficulty in learning mathematics, with special consideration given to students underrepresented in mathematics (particularly women and minorities). Modules focused on concepts and operations for factors, prime numbers, and fractions. Task analysis and demand specification procedures were used to sequence instructional objectives within and across topics. Cognitive social theory provided a framework for the incorporation of attentional, retentional, and motivational variables into the video sequences. Results of field trials show that the modules were effective in teaching/reteaching mathematical skills/concepts to secondary school students who had not made normal progress in mathematical learning. In the first trial, students who used materials gained a significant advantage over control subjects in skills/concepts involving factors and prime numbers. The pattern of gains attributable to these modules was replicated in a second trial, but without a control group. Comparable effects were also found to be associated with use of fractions modules, but these results should be interpreted with caution because of lack of a control group. Additional results indicate that the interactive computer-video modules had a beneficial effect on affective as well as cognitive outcomes. (JN)