Background: Obesity may cause physiological, psychological, social, and economic problems. Therefore, it is of considerable importance to implement preventive interventions for the factors that may cause obesity. Purpose: This study aimed to evaluate the effectiveness of the obesity prevention program developed for secondary school students. Methods: This study was conducted on 116 students assigned to intervention (n = 58) and control groups (n = 58). Data were collected at baseline and on months 6, 12 and 15 after the intervention. Multivariate analysis of variance, t-test with Bonferroni correction and Multi-chi-square test were used for repeated measurements. Results: No significant difference was found in proportions of body mass index classification of children in the intervention group (p = 0.991), while a significant difference was found between measurements on month one and 15 in the control group (p < 0.05). There was no significant difference between mean total scores in the eating behavior questionnaire (p > 0.05). Discussion: In this study, it was thought that it would be more effective to add obesity prevention education to the school curriculum and to keep its duration longer and to include families in this education. Translation to Health Education Practice: Parents play an enormous role in the nutrition of children. Therefore, parents should be supported for a healthy diet in children. Moreover, parents should be included in healthy eating initiatives for children. A AJHE Self-Study quiz is online for this article via the SHAPE America Online Institute (SAOI) http://portal.shapeamerica.org/trn-Webinars