It is proposed that in considering teachers' professional development, emphasis should be placed on teacher assessment as an intergral part of the developmental process, encompassing the total career of the teacher. An overview of the history of teacher evaluation is provided, as well as a review of background literature on professional development. Personal growth and maturation are discussed as being fundamental to the process of professional development. A paradigm is proposed for conceptualizing and studying professional development in such a way that it could lead teachers and researchers to greater effectiveness in facilitating teacher improvement. (JD)