This study investigated the relationships and mean-level changes of middle school students' motivation (expectancy-related beliefs, task values, self-efficacy, and outcome expectancy) toward physical education over time, and how gender affected students' motivation. Participants (N = 206) completed questionnaires over a 1-year period: once in the sixth and seventh grades and again in the seventh and eighth grades. Results yielded that self-efficacy and task values were positive predictors of students' intention across cohorts. The mean levels of self-efficacy decreased over time for students in Cohort 1 (across sixth and seventh grades). However, results revealed a consistent decline in the mean levels of other motivational variables for both cohorts. No gender differences emerged for the variables. The findings are discussed in regard to the implications for educational practice, and future research areas are presented. (Contains 4 tables.)