In this article, I examine my evolving practice and identity as a teacher educator in the context of supervision of student teachers on practicum in schools. As a classroom teacher with approximately 25 years' experience, including mentoring student teachers in my own classroom, I had assumed that when I began working as a teacher educator in the area of school-based professional experience programs it would be a relatively easy and unproblematic transition. This was not to be the case. As I became increasingly involved in practicum supervision, I encountered many situations that challenged my understanding of my work as a teacher educator compared to my work as a classroom teacher. This self-study documents my practice in the so-called third space between schools and universities, for the period of one academic year. I analyzed my journal entries of visits to student teachers on practicum using a theoretical framework of the learning that takes place within boundary spaces between different communities of practice. Results of the study suggested that, in this boundary space, I experienced dynamic and shifting identity construction and re-construction in relation to my former professional identity as a classroom teacher and my relatively new professional identity as a teacher educator. The study also highlighted my changing perspectives on what learning to be a teacher is all about and on the delicate negotiation of relationships that is central to this work.