The opportunities in which university professors collaborate with the practicing school teachers in a teacher study group are few. This study investigated how a university professor facilitated a collaborative teacher study group to enhance teachers' professional growth. Five primary school teachers and a university professor collaborated on incorporating Reader's Theatre into the design and revision of the curriculum in a teacher study group. This study not only identified the roles of the university professor but also highlighted how this outside stimulus facilitated the process of teachers' professional dialogues in this teacher study group. Five roles of the professor in the teacher study group were identified, including content expert, information provider, thought challenger, discussion facilitator, and caring listener. The discrepancies toward the roles that the professor in the teacher study group should serve between the elementary school teachers and the university professor were analyzed and reported. Implications were drawn for both classroom teachers and university professors.