jats:pThe present study aimed to identify factors associated with the Stages of Change (SoC) for physical activity among adolescents who participated in a school-based health promotion intervention. A cross-sectional study was conducted with a sample of 8,071 students whose average age was 13.9 (SD ± 2.4) years. To evaluate the SoC, an adaptation of the questionnaire proposed by Dumith, Domingues and Gigante (2009) was used, considering physical activities performed at least three times per week during 20 minutes. Data collection was carried out from October to November 2013 through self-administered questionnaires in the classroom. The prevalence of students in each stage was: 12.1% in the Pre-contemplation stage, 7.7% Contemplation, 16.8% Preparation, 21.8% Action and 41.6% in the Maintenance stage. Males were more associated with the stages of Action (RR 1.28, 95% CI 1.07-1.54; p = 0.006) and Maintenance (RR 3.57, 95% CI 3.02-4.23; p <0.001) compared to females. Economic level and knowledge about health showed a direct relationship to the Action and Maintenance stages. A large portion of the sample was located in active stages. Being male, being in lower school grades and having a higher index of assets were associated with higher SoC. Knowledge about physical activity and health was directly related to the Preparation, Action and Maintenance stages, pointing to a positive effect on intention or active behavior.</jats:p>