Childhood obesity has reached epidemic levels in developed countries and is showing no signs of abating. The causes of obesity in adolescence are extremely complex, and therefore approaches to prevention and treatments must be multifaceted. Early adolescence is a developmental period when youth are becoming more independent, are influenced by peers, and are making more decisions related to their own health and lifestyles. The purpose of this article is to describe the development, implementation, and evaluation of a multilevel school-based intervention program for middle school students in the Teen Eating and Activity Mentoring in Schools (TEAMS) project. Critical components of success included an interdisciplinary approach, applying available curricula to meet contextual characteristics, and involvement of all stakeholders in planning, evaluating, and refining the program. (Contains 3 figures and 2 tables.)