Childhood overweight is one of the most serious problems currently affecting individual and public health. Schools represent a logical site for prevention because children spend 6-8 hours a day there during most of the year. Although reports of school-based overweight or obesity prevention programs exist, there are no summaries specifying which interventions are effective in preventing weight gain in the school environment. Researchers generally consider randomized controlled trials to be the most reliable and valid findings; so, naturally they are the best for providing evidence on which to base curriculum and policy guidelines. Consequently, the purpose of this paper is to provide an overview of school-based randomized controlled studies intended to prevent increases in schoolchildren's body weight or body mass index. This paper addresses the successes and other positive health outcomes, as well as the limitations of the school-based research. The goal of this paper is to assist school health administrators with curriculum decisions related to overweight or obesity prevention in schools. Following the critique, the challenges of childhood overweight or obesity prevention are discussed, and recommendations for further research, school activities, and policy changes are made.