This dissertation presents a phenomenographic case study of a senior physics professor during and beyond an extended collaboration with a science education professor from a College of Education. The context for the collaboration is the co-teaching of a physics course for graduate students in a Masters of Teaching program at a research university in the southeastern US. The course was focused on physics content and the pedagogy of teaching for conceptual change. The purpose of this study is to investigate from a physics professor’s perspective the progression of his conceptions and practices regarding teaching for conceptual change over the duration of the collaboration and beyond. Prior research indicates that such change is a difficult and complex process requiring a transformative, personal experience. Collaboration between science departments and Colleges of Education has been identified as a key opportunity for transformative experiences, but research on the resulting changes is limited. Questions addressed by this study include (a) what is the evidence of change in a physics professor’s conceptions of teaching for conceptual change, (b) what is the evidence of change in a physics professor’s practices of teaching for conceptual change, (c) what are the learning environment characteristics identified by the physics professor that either facilitated or hindered changes in his conceptions and/or practices in teaching for conceptual change. The primary data were interviews with the physics professor integrated with direct classroom observations. Emergent categories of how the physics professor conceived and practiced teaching for conceptual change showed a progression over time toward a more expert view on teaching for conceptual change. Key factors identified in the physics professor’s progression are: 1) his motivation to become a more effective teacher, 2) the expertise of the science education professor, and 3) the way the collaboration developed. Limiting factors identified include: 1) time pressure for content coverage, 2) difficulty in translating change to other contexts, and 3) unsupportive external environments.