Designed to develop procedures and acquire information to help decision-makers establish policies for the use of microcomputers for computer-assisted instruction (CAI), this study involved the following steps: (1) a school-based research project was conducted to determine the costs and effects of microcomputer-assisted instruction; (2) an analytical procedure for assessing the cost-effectiveness of microcomputer-assisted instruction and traditional instruction was developed; and (3) this analytical procedure was applied to the costs and effects obtained in this study. Subjects were 41 grade 3 students and 38 grade 5 students in a rural area of Saskatchewan, Canada, who were given a pretest to measure mathematics ability, mathematics attitude, and computer literacy. Students at each grade level were then randomly assigned to two groups: the control group received traditional mathematics instruction, and the experimental group received adjunct microcomputer-assisted instruction. On the basis of the findings, it was concluded that the use of supplementary microcomputer-assisted instruction enhanced both the mathematics skills and level of computer literacy of the subjects in the experimental group; there was no significant difference between the effects of the two treatments on student attitudes toward mathematics; and the cost of adjunct microcomputer-assisted mathematics instruction was lower than previous estimates of costs for laboratory-based CAI and more cost-effective than traditional mathematics instruction in relation to the desired outcomes. Seventeen tables are included, 25 references are listed, and additional data are appended. (MES)