The present study investigated how enhancing motivation by delivering positive feedback (a smiley) after a successful trial could affect interference control in adolescents with Attention Deficit Hyperactivity Disorder (ADHD) and in their typically developing (TD) peers. By using a Simon task within the theoretical framework of the “activation-suppression” model, we were able to separately investigate the expression and the inhibition of impulsive motor behavior. The experiment included 19 adolescents with ADHD and 20 TD adolescents in order to explore whether data found in adolescents with ADHD were similar to those found in TD adolescents. Participants performed the Simon task in two conditions: a condition with feedback delivered after each successful trial and a condition with no feedback. The main findings were that increasing motivation by delivering positive feedback increased impulsive response in both groups of adolescents. It also improved the efficiency of impulsive motor action inhibition in adolescents with ADHD but deteriorated it in TD adolescents. We suggest that 1/increased motivation could lead adolescents to favor fast responses even if incorrect, and 2/the differential effect of feedback on the selective suppression of impulsive motor action in both groups could be due to different baseline DA levels.