This digest examines the spread of mentoring in the United States, obstacles to realizing the potential of mentoring as a vehicle of reform, needed research, and selected issues of policy and practice. While the education community understands that mentors have a positive effect on teacher retention, the question of what mentors should do, what they actually do, and what novices learn as a result of mentoring remains open. For example, the culture of teaching encourages autonomy and noninterference; therefore, mentor teachers have little experience with the core activities of mentoring, such as observing and discussing teaching with colleagues. If novices are to learn the ways of thinking and acting associated with new kinds of teaching, they must be placed with mentors who are already reformers in their schools or classrooms and develop collaborative contexts. To inform mentoring policy and practice, comprehensive, empirical research is needed, including studies of mentoring and its effects on teaching and teacher retention, how mentors learn to work with novices in productive ways, what structures and resources facilitate that work, and how mentoring fits into broader frameworks of professional development and accountability. (Contains nine references.) (LL)