Three major purposes have been proposed for Professional Development Schools: (1) to improve education of prospective and practicing teachers; (2) to strengthen knowledge and practice in teaching; and (3) to strengthen the profession of teaching by serving as models of promising and productive structural relations. At present there is neither a fully realized Professional Development School in the country nor a consensus about the mission of such schools. This Digest explores the proposed purposes of these schools and some of the research studies that provided the concepts upon which they would be based. Some critiques of the concept of the schools are also noted. (JD)