Abstract: Objective: The objective of this study was to identify the risk factors that modify food consumption patterns and physical activity in school-age children to encourage a healthy body mass index. Materials and Methods: The study used a quasi-experimental method with a non-equivalent control design. The intervention was implemented for six months in the form of planned group sessions using a peer group model and leaflets. The progress was also monitored on a monthly basis using questionnaires. A proportional random sampling method was used. The data analyses performed were univariate, bivariate and multivariate analyses with Hotelling’s trace and paired t-test. Results: The results of this study show that there was a change in body mass index (p = 0.000), food consumption pattern (p = 0.000) and physical activity (p = 0.001) in both groups. Conclusion: The implementation of the planned peer group session model contributed to the change in nutritional status, eating behaviour and physical activity of the respondents. The parties involved should cooperate to find ways to prevent obesity in school-age children by changing lifestyle habits such as diet and physical activity.