During 1971-72, of 487 students in 2 Introductory Educational Psychology classes, 123 students chose to take a lecture course and 364 students chose a mastery learning class. Despite constraints on interpretation, it was concluded that in this particular situation students acquired a knowledge of vocabulary, principles and concepts at least as well by mastery learning as by lecture-discussion methods. In addition, even in a class of more than 200, in contrast to lecture procedures, the mastery learning procedures provided for vastly increased one-to-one interaction between the student and instructor. More than 90% of the student respondents to an opinion survey felt that mastery learning should continue to be offered as an option for this course. Mastery learning students liked the clarity of goals, the chance to work at their own speed in their own time, and the attainment of course credits by means of unit tests with immediate reinforcement. In contrast to lecture students, many mastery learning students expressed self-change in terms of their own learning processes rather than in terms of course content. (Author/HS)