This study investigated the hypothesis that purposeful activity is an intrinsic motivator. Affecting exertion during the performance of purposeful and nonpurposeful activity was studied in 30 elementary school students. The subjects acted as their own controls in the performance of other exercise. The three experimental exercises were jumping rope, defined as a nonpurposeful activity, and jumping rope with reinforcement, defined as purposeful activity I, and jumping rope with double reinforcement (food), defined as purposeful activity II. Duration and cessation of exercise were entirely controlled by the subject. The number of jumps were measured immediately after cessation of exercise and duration of exercise in seconds by observer. The results were as follows : 1. There was a significant difference in the required time of performance between purposeful and nonpurposeful jumping (p< .05). 2. There was a significant difference in the number of jumps between nonpurposeful and nonpurposeful jumping after reinforcement. (p< .05). Implications for practice and further research are discussed.