This paper reports on a study of the 1980 Maryland State Department of Education school improvement project utilizing Mastery Learning. It examines the instructional process implementation, the impact of one pilot school, and the statewide program through observation, surveys, interviews, document analysis, and participant self-reports. Data were analyzed by site, role, and activity area. The findings are reported for two levels: statewide and within the pilot school. The results indicate that Mastery Learning is effective and appropriate as an instructional improvement process at all grade levels (K-12) and in a wide variety of subjects. Implementation requires considerable time and effort, and teachers expressed dislike for the amount of planning time and recordkeeping required by the program. This study demonstrates that a state department of education can improve instruction with limited financial input and legislation. Significant features of the program include: a cross-hierarchical team training approach; state department of education leadership and assistance; voluntary participation; and a team effort. The author states that Mastery Learning works, but longitudinal studies are needed to determine the cumulative and sustained effect for students. (MD)