This article describes developmentally appropriate activities that can be used in large physical education classes (40+) to teach students about physical fitness concepts. Students should learn the "hows" and "whys" of being physically fit, including health- and skill-related fitness knowledge and the Principles of Training. Some activities in this article were drawn from the "Physical Best Elementary and Physical Best Secondary Activity Guide" (NASPE, 2005a, 2005b). All the activities keep students active, are developmental, and provide students with knowledge about their health and wellness.