The authors investigated patterns of change in three middle grade teachers' beliefs and practices about motivation in mathematics during a yearlong professional development project with a university researcher. Four principles of motivation (and corresponding instructional strategies) were introduced in this sequence: supporting students' competence, belongingness, autonomy, and making learning meaningful. Teachers enacted strategies in their classrooms, were observed and interviewed, and discussed and reflected on results during monthly meetings. Enactment of motivation strategies was related to changes in mathematics instruction for some teachers. Results reflect the importance of situating motivation strategies in content area instruction and providing adequate support for teacher conceptual change. The authors examine both personal and contextual explanations for changing instructional practices and the obstacles to such changes. (Contains 1 note and 3 tables.)