The effects of an individualized mastery instructional system similar to the Keller plan was compared with a conventional lecture-discussion-recitation system in a variety of ways including mathematics achievement and fail rate in the comparison course and subsequent mathematics courses, mathematics reading comprehension, facilitation of performance in other disciplines, student study time, faculty time required for instructional system operation, preference of students and instructors, and student propensity for continued math-related studies. The comparisons spanned 2 years and were carried out under controlled conditions in a balanced, experimental design involving random assignments of 840 students and 12 instructors. In general, the superiority of achievement and attitude outcomes claimed for the Keller plan in many reports was not observed in this study.