The Threshold Concepts Framework acts as a catalyst in faculty development activities, energising and provoking discussion by faculty about their own courses in their own disciplines, and often leading to the discovery of transformational concepts that occasion epistemic and ontological shifts in their students. The present study focuses on faculty development programs where faculty are the students and provides evidence for variation in student learning as a threshold concept that for many faculty members transforms their conceptions of teaching, their identities as teachers, and their practice. A detailed discussion of the pedagogy used to achieve transformational outcomes is provided.