So BMC Public Health 2012, 12:258 http://www.biomedcentral.com/1471-2458/12/258 factors might contribute to school performance. Fourth, this study was a retrospective cohort study; thus, we examined only the interrelation between variables, not cause and effect. However, the subject pool was ex- tremely large and highly representative of the wider Korean population (75,066 subjects residing in Korea). Therefore, these results, derived from the KYRBWS-V, can be considered a valid indicator of the relation be- tween PA and academic performance in Korean adoles- cent students. Conclusions We conclude that vigorous PA undertaken less than 4 times a week was positively correlated with academic performance in the case of boys, and moderate PA was positively correlated with academic performance in both boys and girls, in the adolescent Korean population. However, strengthening exercises were not positively correlated with academic performance in boys or girls. Furthermore, when performed 5 or more times a week, vigorous PA in boys and strengthening exercises in both boys and girls were negatively correlated with academic performance. Adequate PA can provide health benefits and play a vital role in weight control and reducing the risk of chronic dis- eases. Furthermore, this study shows that physically active adolescents are more likely to perform better at school. On the basis of the results of this study, we suggest that health-care providers incorporate PA in the students’ time tables and encourage them to be physically active and con- sequently improve academic performance. Competing interests The author has no competing interests. Acknowledgements This work was supported by a special research grant from Seoul Women’s University (2012). Author’s contributions W-YS contributed to study design and management, performed statistical analyses and drafted the manuscript. 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