In this study we examined the interrelationship among extrinsic rewards and achievement goals (including a work-avoidance goal), competence beliefs, and task values associated with health-enhancing running tasks over a school year. A group of elementary school students (n = 119) from a program that promoted running for running's sake and another (n = 88) from a program that promoted running through games provided pre- and post-year data on students' achievement goals, competence beliefs, task values, achievement in running tests, and future intention to continue running as a health-enhancing activity. Results showed that students in the running-for-games program demonstrated significant growth in task-involved achievement goals. The regression analyses showed that extrinsic reward and selected intrinsic motivation constructs played a small role in predicting running-test scores. Interest, however, emerged as the most important intrinsic motivation construct for predicting future motivation for running. Interest seemed to override the effects not only of extrinsic reward but also of other intrinsic motivation sources. This finding suggests that interest-based motivation sources might have a strong and prolonged effect on learner motivation.