Regular exercise boosts teenagers' school grades - and particularly helps girls in science, a British study finds.
The more physically active they were, the better children performed in school, according to findings published online in the British Journal of Sports Medicine.
Physical activity has long been thought to boost brainpower.
For the study, researchers from Britain and the United States measured the level of physical activity among nearly 5,000 11-year-olds, who wore a motion-reading "accelerometer" for a week.
Their performance in English, maths and science was then assessed at the ages of 11, 13, and 16.
Children who had been more physically active at 11 performed better in all three phases and all three subjects.
Every 17 minutes of exercise per day at the age of 11 led to an additional improvement in marks for boys, and 12 minutes per day for girls by the age of 16.
The effect was noticeably large for girls in science classes.
Worryingly, the researchers observed that aged 11, boys averaged 29 minutes of moderate-to-vigorous exercise per day and girls about 18 - far lower than the recommended 60 minutes.
"Their findings prompt the authors to speculate on what might happen to academic performance if children increased the amount of moderate-to-vigorous physical activity they did to the recommended 60 minutes," said a press statement.