The Time for Mastery Program was specifically designed to minimize the time costs of mastery learning by maximizing the use of instructional time to the fullest advantage. The program was implemented by three high school districts in suburban Chicago during the 1984-85 academic year. This article presents a brief description of the program, as well as a report of the outcomes realized thus far, and a discussion of implications for the design of staff development programs. The program is delivered through a five-day summer seminar and three on-day follow-up sessions during the first semester of school. In addition to the summer seminar and the follow-up sessions, the teachers are also trained in peer observation and coaching. The focus of the program centers on the positive alteration of two variables: instructional time and testing practices. The content of the program reflects a combination of instructional practices drawn from the findings of the research on classroom management and mastery learning. It is noted that one of the key factors that can be attributed to the success of the program is the commitment of time for staff development. (JD)