Formal mentorship programs are growing rapidly, from large corporations to school districts.  Firms and organizations make substantial investments to support these mentorship programs, yet there is little evidence that mentorship programs improve employee retention, performance or subsequent career advancement.  One reason that empirical evidence on mentorship impacts is hard to come by is that most mentorships form voluntarily.  While there may be advantages in allowing mentors to select their protégés (or protégés to select their mentors), the inherent self-selection makes it impossible to assert that mentorships cause heightened productivity or more rapid advancement.  When mentor relationships form voluntary, it is possible that employees selected for mentoring would have exhibited higher performance and more rapid career advancement even in the absence of the mentorship. 

To overcome the inherent selection in voluntary mentorships, we focus on officers serving in the United States Army.  Mentors in our study are battalion commanders, and their subordinate company commanders are protégés.  Every company commander is assigned to a battalion (and hence a battalion commander mentor).  These mentorships typically last roughly 18 months, and involve daily interaction between mentors and protégés.  Within occupational branches of the United States Army, officers assigned to company command report to a military post, and then report to a specific military unit.  Mentor-protégé relationships are formed based purely on the needs of the Army; the characteristics of individual battalion commanders and company commanders do not guide assignment decisions.  Army personnel policies provide a unique opportunity to measure the impact of mentorships in an environment in which all subordinates are given mentors by a process that is as good as random.

 We study the differential impact of high performing mentors on the subsequent career advancement of their protégés.  We define a high performing mentor as a battalion commander who was promoted early to the rank of Major.  Early promotions to Major are granted to roughly one-in-eleven officers who go before a centralized Army promotion board, and take place several years prior to a Lieutenant Colonel serving as a battalion commander.  The subsequent career advancement we study for our protégés is whether they are selected for early promotion to the rank of Major.  This promotion decision occurs after the formal mentoring relationship with their battalion commander ends. 

The impact of serving under a high performing mentor raises a company commander’s likelihood of early promotion to Major by nearly 29 percent. We also find that the likelihood of early promotion increases as time spent with a high quality mentor increases.  Serving under more than one high performing mentor does not result in an additional increase in the likelihood of early promotion.  The impact of a high performing mentor is greatest for high ability protégés.

Mentorships potentially shape protégés through many different mechanisms, including: human capital formation, signaling performance potential, access to professional networks, selective attention, role model effects, and  the transmission of organizational values.  Our findings are consistent with several of these mechanisms, although we cannot isolate the relative importance of each.