Programed mastery learning materials on matrix algebra were studied by 59 eighth-grade boys. Both experimental and control groups were divided into high- and low-ability groups. The experimental group reviewed all three instructional units until students achieved mastery, but the control group reviewed only Unit 3. Test scores of the treatment group increased over the sequence, especially between Units 1 and 2 and Units 1 and 3. Scores of the control group decreased. High-ability students scored higher in both groups, but the difference between the three units was not influenced by ability or by a combination of treatment and ability; the treatment was equally effective for both levels of ability. There was no difference in time spent learning Unit 1 by treatment vs. control groups. The treatment group spent significantly longer learning Units 2 and 3, but review time decreased from Unit 2 to Unit 3. The control group required more time to learn Unit 3 to mastery than the treatment group. Treatment aided the learning efficiency of the low-ability students, as well as retention of the materials ten days later. (GDC)