Do extra compulsory physical education lessons mean more physically active children - findings from the Childhood Health, Activity, and Motor Performance School study Denmark (The CHAMPS-study DK) - Møller, N. C.; Tarp, J.; Friis Kamelarczyk, E.; Brønd, J. C.; Klakk, H.; Wedderkopp, N. (International Journal of Behavioral Nutrition and Physical Activity, 2014)