Mastery learning is a behavioral instructional method using additional learning time and repeated testing opportunities to increase student learning. A quasi-experimental group design with repeated measures was used to contrast mastery learning and nonmastery learning instruction for 137 undergraduates in 4 sections of an introductory social work course. One instructor taught two course sections with mastery learning, and another instructor taught two sections with nonmastery learning, but the sections had identical content, examinations, and texts. Dependent variables included achievement and retention of learned material, attitude toward course topic, instructional preference, and instructor hours spent. Both methods resulted in similar achievement, retention, instructor hours spent, and changes in attitude toward course topic. All of the students (100%) preferred the mastery instruction. Mastery learning should be considered a promising instructional method for social work education. (Contains 1 figure, 8 tables, and 65 references.) (Author/SLD)