Objective: To evaluate the short-term outcome of the social marketing approach used in Project FIT, we developed a school- and community-based programme for promoting healthful eating and physical activity in kindergarten to 5th-grade children and their parents. Design: A 2-year quasi-experiment for children and two cross-sectional surveys for parents. Setting: We included low-income, urban and ethnically diverse elementary schools and neighbourhoods in Grand Rapids, Michigan, USA. Method: Students in 3rd, 4th and 5th grades were surveyed in four intervention schools (four time points, N with at least one time point measurement = 664) and two control schools (N = 195). Parents of intervention students were surveyed at baseline (N = 286) and follow-up (N = 215). Key dependent variables included self-reported healthful eating and physical activity. Key independent variables included awareness, knowledge, motivation and attitudes towards Project FIT. Analysis: We analysed generalised linear mixed models and generalised estimation equation (GEE) models for the student surveys and mean difference tests and logistic regressions for the parent surveys. Results: The proportion of students who were aware of Project FIT increased over time. GEE models showed that selected key dependent variables were significantly associated with self-reported healthful eating and physical activity. Parents were more aware of Project FIT at follow-up compared to the baseline survey, and their attitudes were significantly associated with increased healthful eating (vegetables, fruits and whole grains). Conclusion: The social marketing approach utilised in Project FIT contributed to increasing awareness and achieving behavioural goals of healthful eating and physical activity.