Using a quasiexperimental design, the authors examine whether fourth- and fifth-grade students exposed to a developmental physical education (PE) curriculum, Michigan's Exemplary Physical Education Curriculum (EPEC), demonstrated stronger motor skill--specific self-efficacy and perceptions of physical activity competence, physical activity levels, motor skills, and physical fitness than did students exposed to existing PE curricula. The authors conducted a multilevel regression analysis with data from 1,464 students in the fourth and fifth grades. Data were collected using a student survey, an activity checklist, and motor and fitness assessments. Compared to students receiving standard PE, students exposed to EPEC showed significantly stronger results in motor skills but not fitness outcomes. The authors found significant positive intervention effects on indicators of motor skill self-efficacy and physical activity levels among the fourth-grade cohort. EPEC was more effective than standard PE curricula at improving motor skill performance (fourth- and fifth-grade cohorts) and at increasing self-reported motor skill-specific self-efficacy and physical activity (fourth-grade cohort). (Contains 2 tables.)