Want your child to have better grades? Maybe she needs more time at the playground.

A new study has flipped the old stereotypes about dumb jocks and out-of-shape nerds on their heads, finding that it's actually the kids who exercise more who do better in school than their peers. The research, which was published in the Journal of Pediatrics, compared standardized test scores for 4th to 8th graders in public schools in Lincoln, Nebraska with each child's fitness level and BMI - or Body Mass Index. Researchers found that elementary and middle school students who don't get enough exercise are more likely to fail math and reading tests. On the other hand, physically fit children had a 2.4 times greater chance of passing math tests and a 2.2 times greater chance of passing reading tests compared to their less fit peers.

The study was undertaken in response to the recent trend at many schools, including the public schools in Lincoln Nebraska, where gym classes and recess have been cut to give students more time to focus on academic pursuits.

“Although the long-term consequences of childhood obesity are well documented, some school districts have reduced physical education classes to devote more time to the three Rs in education — reading, writing, and arithmetic,” said that study's lead researcher Dr. Robert Rauner of Creighton University and Lincoln Public Schools. “However, there is new evidence that leaving out an important fourth R -- aerobics -- could actually be counterproductive for increasing test scores. Schools should think twice before taking minutes from physical education classes and recess,” Rauner warned.

Researchers also found that while BMI is a factor in a child's overall health, it did not have a significant effect on test scores, indicating that it is aerobic fitness and not necessarily body fat or obesity that effected school performance.

Does your child's school still encourage physical education and recess? Do you think it affects your child's academics?

Fit kids do better in school, study finds
Study finds that less fit kids are more likely to fail math and reading tests than their aerobically fit peers.