In efforts to enhance pre-service teachers' preparation for the profession, the establishment of formal partnerships between schools and universities is now a mandated requirement for the accreditation of initial teacher education programs (AITSL, 2016). However, building successful partnerships is far more complex than merely signing partnership agreements, and requires a willingness for personnel in both sites to cross institutional boundaries and co-create new understandings and ways of working. In this paper we focus on the shifts of thinking that occurred for five mentor teachers, involved in a Teaching Academies of Professional Practice (TAPP) project in Victoria, as we forged new ways of providing professional experience programs. Interview data is used to explore the development of the teachers' agency and identity as they participated in professional learning activities to unpack theoretical understandings of teacher education and co-created new professional experience practices alongside university-based teacher educators. This paper uses the theoretical ideas of boundary spaces and boundary crossing mechanisms (Akkerman & Bakker, 2011) and Dialogical Self Theory (Hermans, 2013) to discuss how repositioning mentor teachers as fellow teacher educators allowed for expansions in the understanding and enactment of their role. The mentor teachers were able to articulate how their perceptions of mentoring had moved from being largely concerned with assessing pre-service teachers' performance and evaluating fitness for the profession, to a more educative focus of supporting pre-service teachers to build deep understanding of what teachers do and why. By seeing themselves as 'teachers of teaching' they drew on their existing strengths as classroom teachers, concerning themselves with nurturing the pre-service teachers' learning and well-being, as they do with their own students in their classrooms. This reimagining of the mentoring role became possible because all personnel in the partnership committed to creating a 'boundary space' in which the expertise of all participants was valued and respected. Considerable time and effort was put into understanding each other's different contexts and building shared goals and new practices for supporting the development of pre-service teachers. Several of the mentors reported that these new practices of explicitly articulating and unpacking their teaching with pre-service teachers also enhanced their own learning and confidence in both mentoring and their own teaching. The findings of this study suggest that partnerships between schools and universities can therefore enhance learning opportunities for all participants when commitments are made to creating genuine boundary spaces which support new ways of working together.