This positioning paper seeks to contribute to the knowledge base of the changing professional learning needs of supervising or mentor teachers in initial teacher education. To do so, we draw from the work of "Project Evidence," an Australian Office of Learning and Teaching funded project, designed to support teacher education through the development of a professional learning website. Our focus in this paper is our growing understanding of the complex work of teachers as they navigate new supervisory and mentoring roles in the current education context of high stakes standardisation. We examine the implications for their changing work practices within the policy imperative to build effective school-university partnerships in teacher education. Within this context, we discuss the ways in which Project Evidence has attempted to (re)position the emphasis of the work of the mentor teacher away from the dual role of assessor and supervisor to encompass their own professional learning.