Two field trials were conducted to test the effectiveness of instructional materials, which were presented on an Apple II Plus microcomputer interfaced with a videocassette recorder, in teaching mathematical skills to students who had not made normal progress in mathematics learning. In the first field trial, 58 experimental students from a high school with a high proportion of Hispanic students participated in modules covering instruction in factors and prime numbers. A criterion-referenced pre- and posttest and a School Learning Questionnaire (SLQ) were administered to both the experimental students and to 43 control students. A second field trial retested the factors and prime numbers modules and provided a pilot test of a fractions module. The subjects were 11 volunteers from an alternative school remedial program for students who had failed to pass the basic skills competency test required for high school graduation. Pre- and posttests were again administered. The results of the field trials showed that the computer-video instructional modules were effective in teaching or reteaching mathematical skills to secondary school students. However, the hypothesis that exposure to the instructional materials would be reflected in an increase in effort attributions specific to mathematics was not supported. A 38-item bibliography accompanies this report. (ESR)