Purpose: This study aimed to determine the extent to which a concept-based physical education curriculum, specifically the Science of Healthful Living (SHL) curriculum, influenced middle school students' knowledge, motivation for physical education (PE) and physical activity (PA), and out-of-school PA. Methods: A static group comparison design was adopted to analyze the differences on fitness knowledge, autonomous motivation for PE and PA, and out-of-school PA between eighth-grade students who studied the SHL curriculum (the experimental condition, n = 168) and their peers who studied a multiactivity PE (the control condition, n = 226) 1 year earlier. Results: The students who studied the SHL curriculum demonstrated significantly higher levels of knowledge (p < 0.05, Cohen d = 0.81), autonomous motivation toward PA (p < 0.05, Cohen d = 0.20), and out-of-school PA (p < 0.05, Mann--Whitney U effect size = 0.01) than students who had experienced the multiactivity PE. The students in both conditions were equally motivated in their respective PE courses. Conclusion: The SHL curriculum is effective in promoting students' PA behavior outside of the school.