Human Anatomy and Physiology courses are "gateway" courses that students must pass with high grades in order to proceed through their program of study. However, student pass rates are often low, resulting in students attempting the course multiple times and delaying their graduation. Supplemental instruction performed by peer leaders is one mechanism that has been used to increase student success. The goal of this study was to evaluate the effectiveness of peer-led supplemental instruction by comparing predicted and actual course grades. We learned that students predicted to earn a C achieved higher grades when they utilized supplemental instruction. While those students performed better than predicted, supplemental instruction did not improve ABC rates for the class. We conclude that supplemental instruction can be of benefit for some students.