Childhood obesity is a serious public health problem with limited effective prevention strategies to date. Although previous nutrition and physical activity environmental approaches for obesity prevention show some promise, most studies have not shown reductions in excess weight gain. Moreover, few prevention studies significantly engage parents and focus on the home environment. To prevent childhood obesity it is essential to promote healthy behaviors in the home environment because parents are influential primary role models for healthy eating and sedentary behavior, and are gatekeepers for food and beverage availability and degree of inactivity within the home. Moreover, the home setting is where most of children's calories and energy dense foods are consumed and where children engage in much of their sedentary behavior, particularly screen time (e.g., television, computer, game system). The proposed study will test the efficacy of the Healthy Home Offerings via the Mealtime Environment (HOME) Plus program, a ten-month, family-based health promotion intervention to prevent excess weight gain among 8-12 year old children. The program is based on Social Cognitive Theory and a socio-ecological framework and promotes both regular and nutritionally-sound snacks and meals in which family members eat together (i.e., family meals) and encourages reductions in sedentary behavior, particularly screen time among children in the home setting. The efficacy of the intervention will be tested in a randomized controlled trial with 160 families randomized to two conditions (intervention or attention-only control). Two cohorts of families, recruited from after-school programs and community centers, will be followed for 2.5 years. The primary hypothesis is that, by the end of the ten month intervention, target children in the intervention families, relative to children in the control families, will have significantly lower body mass index (BMI; primary outcome) after adjustment for baseline BMI values. Secondary outcomes include frequency of weekly family meals and number of healthful foods and beverages available in the home and served at family meals and snacks (as reported by parent), target children's daily intakes of healthful foods and beverages, and target children's minutes of sedentary behavior per week, particularly screen time. Child and parent measurement will occur in their homes at baseline, post-intervention (12-months post-randomization), and follow-up (9-months post-intervention) by trained research staff. The proposed study builds upon successful methods from our HOME pilot study (2006-2008; NIH R21-DK0072997) and is innovative as it actively engages entire families in experiential activities and capitalizes on the home setting. The study will provide important information on environmental and behavioral strategies that families can use at home to prevent excess weight gain. The intervention program has high translation potential and is likely to be immediately useful to families of school-age children because it will be tested in real-world community settings and sustained across the state of Minnesota by the University of Minnesota's Extension Service.