This paper documents one university's use of action research to encourage preservice teachers' ongoing critical reflection as they negotiated diversity and community in their classrooms. Several supervisors developed a self-study research plan, meeting over 1 year to study several strategies for engaging preservice teachers in critical reflection. Preservice teachers were required to participate in a community project that was a natural extension of student teaching. Data were collected from meeting notes, journal entries, sharing sessions, interviews, supervisory journal entries, feedback cards from peers, and final reports. Researchers analyzed the impact of action research participation on student teachers' critically reflective practice and understanding of external communities. As participants examined more closely their students and classrooms, they began critically viewing their situations and dealing constructively with their concerns, considering them as possible action research topics. Student teachers discussed their action research questions and strategies in class, then designed their investigations, which examined the effects of particular teaching practices on certain students. In weekly seminars, they shared their strategies and challenges. As students changed classroom placements each semester, their action research changed focus. Students came to a greater understanding of their classroom community by participating in the project. They learned to view teaching itself as a form of inquiry or experimentation. (Contains 52 references.) (SM)