Research on learning to teach repeatedly cites the disjuncture in teaching practices promoted across universities and K-12 schools. Much of the literature that is focused on this "two-worlds pitfall" (Feiman-Nemser & Buchmann, 1985) describes the influence of cooperating teachers' more traditional teaching practices on teacher candidates' developing practice. This article, however, provides a case study of a student teacher whose commitment to social constructivist practices was reinforced by the intersection of competing views of teaching and mentoring that collided during her student teaching. We highlight the significant impact of the cooperating teacher's approach to mentoring--more so than teaching--on a student teacher's developing practice. We conclude with recommendations for supporting student and cooperating teachers to develop shared understandings of the purpose of student teaching and mentoring and to engage in educative dialogues about teaching that support the cross-institutional negotiations inherent in mentoring and learning to teach.