The purpose of this formative evaluation was to examine the impact of an innovative inquiry-based science education curriculum for middle school students, called Choice, Control, and Change, that is designed to foster healthful eating and physical activity and a healthy weight through enhancing agency and competence. The 24-session curriculum helps students develop understandings about the interactions between biology, personal behavior, and the environment and personal agency through cognitive self-regulation skills in navigating today's complex food system and sedentary environment. An extended theory of planned behavior served as the design framework. The study used a pretest-posttest evaluation design involving 278 middle school students in 19 science classes within 5 schools. Based on paired t tests, students significantly improved on several curriculum-specific eating and physical activity behaviors: they decreased several sedentary activities and increased their frequencies of fruit and vegetable intake. They decreased the frequency of sweetened beverages, packaged snacks, and eating at a fast-food restaurant, and ate and drank smaller portions of some items. Their outcome beliefs and overall self-efficacy, but not their attitudes, became more positive. A strategy based on fostering personal agency, cognitive self-regulation, and competence can be effective in increasing healthful eating and physical activity behaviors in middle school children and should be explored further. (Contains 3 tables.)