Ragins, B.R., Cotton, J.L., & Miller, J.S. (2000). Marginal mentoring: The effects of mentor, quality of relationship, and program desing on work and career attitudes. Academy of Management Journal, 43(6), 1177-1194.
I really nice study that looks at the effects of having a mentor (vs. no mentor), different types of mentoring and the quality of the mentoring relationship. Nice discussion piece for in class and demonstrates what needs to be considered when implementing mentoring in an organisation.