The theory that there are stages in teachers' professional development suggests that those who aim to stimulate or support that growth must be sensitive to the stage each teacher is in. Three stages of development are described: the survival or beginning teacher stage; the middle stage, characterized by an increasing sense of comfort in the teacher role; and the mastery stage, characterized by a sense of confidence and ease. Teachers' center experience indicates that the formal and traditional forms of inservice programs decrease in value as teachers increase in mastery. Workshops and how-to courses are valuable to most first-and second stage teachers, but helpful only occasionally for third-stage teachers. (JD)