Focusing on eight instances of experienced and beginning teachers' work together in junior and senior high schools in a large urban district, this study explores the work of experienced teachers with beginning teachers, experienced teachers' perceptions of their role, and subsequent enactments. Mentors pass on to beginning teachers, through their teaching and discussions with the beginning teachers, many messages about teaching and learning in an urban context. Yet, as with the existing but often competing and conflicting rules that govern junior high dances and lead to uncertain expectations and outcomes, there are conflicting ideas about what mentoring is supposed to lead to. Most notable in the data are conflicts mentors experience in fitting role expectations with role enactment and the difficulties of criticizing beginners' teaching practices. Two conditions of the work, the limited time available to mentors and the norms governing the work, add to the conflicts. An implication of the study is that mentors could provide a model for beginning teachers by showing how their own struggles to overcome the dilemmas of their practices result in worthwhile experiences in which they study and learn about teaching over time. (JD)