The relationship between instructional treatment manifested as mastery learning and non-mastery learning strategies and various measures of Spanish proficiency was studied with 41 freshmen at an all-female high school in the New Orleans (Louisiana) area. Subjects were grouped homogeneously into 2 classes of 22 and 19 students, representing the experimental group that received mastery learning instruction and the control group that received conventional/non-mastery learning instruction, respectively. Dependent variables of degree of learning as indexed by achievement scores, perseverance on assigned academic tasks, and time required to criterion were examined in the context of a non-equivalent, matched control group, pretest-posttest design. Analysis of covariance and correlated groups t-tests suggest significant achievement scores and time invested favoring the mastery approach, but non-significant differences regarding perseverance. The provision of feedback-correction procedures via diagnostic formative trial tests and the learning corrective prescriptions appears to be a key element in the effectiveness of mastery learning as an instructional delivery system. Five tables present study data. (SLD)