Regular exercise can boost teens' grades, according to a study CBS News reported.

New research found that children's' grades increased in direct correlation with the amount of physical exercise undertaken in the average day.

"Our study suggests that the effect of physical activity may be quite large," John Reilly, a professor of physical activity and public health science at the University of Strathclyde in the U.K. told Bloomberg News.

They found that children and adolescents who routinely engaged in moderate to vigorous exercise had long-term improvements in their academic performance.

The more children exercised at age 11, the better they did in school. They also did better at 13, and at 15 to 16. Performance at age 15 to 16 rose for every extra 1 minutes of exercise for boys and every 12 minutes for girls, My San Antonio reported.

Researchers looked at a sample of about 5,000 schoolchildren who were enrolled in a long-running study that tracks children born in the U.K. between 1991 and 1992, CBS News reported.

Because even the most active children got less than 60 minutes of exercise a day, the effect is speculative.

"The actual levels of daily physical activity at age 11 were quite low," Reilly said.

When children reached the 11 years old, their daily physical activity levels were measured using an accelerometer for three to seven days. The device, similar to how a pedometer tracks steps, recorded the average time children exercised, which was 29 minutes a day for boys and 18 minutes for girls.

The children had their academic performance tested at ages 11 and 13 with compulsory national tests for students, and also at 15 or 16 with the General Certificate of Secondary Education (GCSE) exam. The tests judged the children's abilities in English, math and science subjects.

Researchers adjusted for factors likely to influence academic success, such as socioeconomics and the child's current weight.

The researchers couldn't pinpoint how exercise pushes academic achievement, but the effect was most pronounced for girls in science, pointing to a possible gender difference in the way activity affects female brains.

The World Health Organization recommends an hour of moderate to vigorous exercise daily for children from age 5 to 17.