Developing mentor support can become a major financial investment for a school district. Inservice programs must be implemented to develop the mentors. Additionally, in order to serve new teachers, the mentors must be released from their classroom duties through the use of substitute or full-time replacements. To protect the investment of district funds and mentor time, mentor preparation programs must be able to develop effective mentors. The ultimate benefit of mentor effectiveness is increased effectiveness of beginning teachers, which has long-term payoffs for districts and their students. While much attention focuses on the retention of teachers as a measure of induction success, mentor teachers and their abilities have received little recognition. There appears to be no research that studies the impact of mentor preparation programs on specific mentoring abilities. Those developing mentor preparation programs in addition to those districts utilizing them have a need for additional measures of program effectiveness. This paper reports on the impact of induction on mentors as indicated through the measurement of mentor efficacy beliefs. The Mentor Efficacy Scale is included. (Contains 13 references.) (CCM)