The major purpose of this study was to compare self-instructional mastery and nonmastery treatments to determine if there are differences in learning, retention, and time-to-testing of high, middle, and low aptitude students. Twenty grade 7 classes from the Savannah-Chatham County School District served as the experimental population. Students were tested for placement in one of three levels of aptitude; then, classes were randomly assigned to two groups and treatment was randomly assigned to groups. The nonmastery treatment received a student text and a workbook which contained prescribed activities and a single review test for each chapter. The mastery treatment received the same student text; however, the chapters in the workbook contained two review tests. If the criterion level was not attained in the first review test, mastery students were required to correct and relearn material and then take a second review test. A multiple choice test and recall test was administered to measure learning and retention of the content materials. Findings showed that differences in aptitude were not reduced when self-instructional materials were used. An implication of this study is, however, that the lack of teacher monitoring in administering the review tests may have contributed to the poor performance of low aptitude students, since typically low aptitude students require close supervision. (Author/ND)