This study examines the mentoring relationships of student instructors who provide supplemental instruction for undergraduate science courses. Specifically, we examined the relationships negotiated between mentor and protege student instructors during the first year of the mentoring program. The undergraduate student instructors in this study are part of a Supplemental Instruction (SI) program that focuses on helping undergraduate students who are enrolled in science courses that are often labeled as traditionally hard courses. To support the new undergraduate student instructors in the SI program, a mentoring model was implemented to encourage collaborations with other undergraduate student instructors in the SI program. (Contains 2 tables.)