Motivation is critical to the quality of student engagement and achievement in school. A great deal of research has examined children’s motivation in physical education, but most of it is cross-sectional. It has been suggested that longitudinal work is needed if we wish to better understand how motivational processes evolve in children. The present study, therefore, employed a longitudinal design to examine children's motivation and performance in required running programs conducted during their regularly scheduled physical education classes. Specifically, using the expectancy-value model of achievement choice (Eccles, 1998) as a theoretical framework, this study examined whether mean levels of children's expectancy-related beliefs, subjective task values, intention for future participation in running, and their mile run changed over time. Participants (56 boys and 40 girls) completed a timed mile run and questionnaire three times over a two-year period: twice in the fourth grade (September and May) and once again in May of the fifth grade. The 13-item, 5-point scale questionnaire, adapted from previous work with elementary children, assessed children's expectancy-related beliefs, subjective task values, and intention for future participation in running. A repeated measures multivariate analysis of variance yielded a significant main effect for time, Wilks' l = .23, F (8, 87) = 36.12, p < .001 and no significant effect for gender. Univariate analyses revealed that a significant time effect existed on expectancy-related beliefs (p < .02), subjective task values (p < .019), intention for future participation in running (p < .001), and the mile run (p < .001). Post hoc tests indicated that children's expectancy-related beliefs remained the same throughout the fourth grade but decreased by the end of the fifth grade. Children's subjective task values increased during the fourth grade but decreased by the end of the fifth grade. Children's intention for future participation in running declined across the fourth and fifth grades. Conversely, children's mile run improved across the fourth and fifth grades. Overall, results of this study indicate that children improved their mile run but became less motivated for running as they progressed through grades 4 and 5. To counter this motivational downward trend, researchers and teachers must work together to find strategies that maintain and enhance children’s motivational levels if running programs are to remain as part of the physical education curriculum in many schools.Keyword(s): elementary education, physical activity