Cooperating teachers play a vital role in the professional development of student interns. Although they serve as mentors, most cooperating teachers do not receive comprehensive or coordinated preparation for their role as effective mentors. This article presents findings from a qualitative research study exploring the perceptions of nine cooperating teachers about mentoring student interns and identifies the salient factors impacting their mentoring relationships: (a) role of the mentor, (b) expectations for the mentoring relationship, and (c) cooperating teachers' motivation for serving as a mentor. A formal mentoring preparation program was designed for cooperating teachers and implemented at our university. The Summer Mentor Teacher Support Program (SMTSP) consisted of a two-day, 6-hr-per-day workshop, which addressed strategies for effective mentoring and building positive relationships and served as the site for data collection. A brief description of this program is provided. (Contains 1 table.)