Supplemental instruction using peer leaders can assist student learning in undergraduate STEM courses, but optional sessions are not well attended. This study compared attendance in peer leader sessions, nonproductive grade rates, and student evaluation data across two Human Anatomy and Physiology I courses in two different years. One course included peer leader session times that were posted at the start of the semester along with course schedules and incentives for attendance. In the other course, peer leader session times were scheduled after the start of the course without additional incentives for attendance. Incentivizing students and pre-planning peer leader sessions was associated with 70.4% of students attending at least ten weeks of peer leader sessions and a modest decrease in nonproductive grades. By comparison, 9.6% of students attended peer leader sessions in the course that lacked pre-scheduled sessions and student incentives. Future planning should include assessments of student learning and critical thinking associated with the peer leader program.