Purpose: This study evaluated the effects of a goal setting intervention on aerobic fitness (AF) in 6 to 8 grade students. Method: Students at the intervention school received a lesson on SMART goal setting. Students in the comparison school served as a measurement-only group. AF was assessed via the PACER multi-stage shuttle run test pre and post intervention. Between-group differences for change in AF were assessed using a RM ANCOVA. Results: A significant group by time interaction was observed for PACER performance, F(1,263) = 39.9, p < 0.0001. Intervention students increased PACER performance from 40.6 to 45.9 laps, while comparison students exhibited a decline from 30.2 to 23.4 laps. Intervention students were 10 times more likely than those in the comparison school to maintain Healthy Fitness Zone status or progress from Needs Improvement Zone to Healthy Fitness Zone. Discussion: Educating middle school students about SMART goal setting may be an effective strategy for improving aerobic fitness.