Mastery learning is described as a system for providing a unit-by-unit sequence, and arranging that each unit be successfully mastered by each student before they begin the next unit. This process requires mastery tests to control the rate of student progress. The proper setting of score levels to represent mastery is a difficult task. The claim is made that, although group-based mastery learning may often delay the progress of the faster students at first, eventually the general result tends to be more efficient for learning for all students as compared to other group instructional processes. Bibliographical references are appended. (Author/CTM)