Mentoring is often portrayed as an unqualified good. Teacher educators claim that mentoring holds promise for beginning teacher development, increased retention of novice teachers, and mentor-teacher improvement. Drawing on positioning theory, this study describes negotiation of power and position in a failed triad composed of a public school mentor, a university mathematics supervisor, and an intern teacher. Data reveal how each member of the triad sought to make sense of his or her experience and to accomplish desired aims. The activity of positioning and being positioned within the triad profoundly shaped each participant's experience and ultimately interfered with the intern's induction into teaching.