Objective To provide 1-year outcomes for a randomized controlled trial of a behavioral-educational intervention for the primary prevention of osteoporosis among 247 preadolescent girls. Methods Girl Scout troops were randomly assigned to one of two intervention groups–a group comprising girls only (n = 73) and girls with their mothers (n = 94)–and a healthy-lifestyles control group (n = 80). Multilevel (hierarchical) models were employed to account for clustering of girls within troops. Results Among girls who met the recommended levels of Ca at baseline, those in the intervention were significantly more likely to maintain or improve their intake at follow-up compared to controls. No significant group differences were found for changes in WBPA. Conclusions A behavioral intervention for the primary prevention of osteoporosis holds promise for maintaining adequate Ca intake among preadolescent females.