We used border crossing as a theoretical framework to explore the tensions that developed between two mentor-intern pairs during the course of a yearlong internship in high schools in the United States. Interviews with mentors and interns, and observations of planning sessions, teaching episodes, and follow-up conferences indicated that differing conceptions of mentoring, expectations related to communication, and beliefs about teaching formed the primary borders that the pairs had to navigate. Findings from the study suggest that the university must take a greater role in fostering communication between mentors and interns, and in providing on-going support to mentors engaged in teacher education. (Contains 1 table.)