Schools which have successfully implemented mastery learning (ML) programs show many similarities in their plans for ML development. These similarities stand out so strongly that knowledge of them can help all schools in planning for ML. The following program commonalities observed during visits to several schools in New York, Washington, Colorado, and Oregon are: (1) change to ML based upon an identified need; (2) initial involvement and dedication of a head administrator; (3) formal board action indicating dedication to ML ideals; (4) evolutionary (slow, methodical) program development; (5) involvement and commitment of teachers; (6) extensive and ongoing staff development; and (7) revision or re-examination of staff evaluation procedures. A true ML program will do the following: diagnose and teach prerequisite skills; teach in two or more modes to an objective; use formative tests to give feedback to teacher and student; reteach using correctives, time, and a new teaching mode; and use criterion-referenced tests for summative evaluation of mastery. (EM)