This study investigated the effects of mastery learning on learner achievement in the psychomotor domain and also sought to identify the specific learner who might benefit from the use of mastery learning techniques. Subjects were college students learning to play racquetball. Fourty-three students were assigned to three intact mastery classes, and forty-four to three intact non-mastery classes for a period of twelve weeks. A repeated measures analysis of covariance revealed the following major findings: (1) the achievement of the mastery group was significantly higher than the non-mastery group at the mid-test; however, in the post-test, the groups were statistically equal; (2) in particular, low aptitude students, females, and especially the low aptitude females benefitted from the conditions provided by mastery learning methods; and (3) the conditions provided by mastery techniques produced some less than positive attitudes about grading and the class in general. (Author/JD)