All work and no play really does make Jack a dull boy. The cure for it seems to be physical play, not video games.

In a study of overweight children, regular exercise improved their scores on intelligence tests and math ability. Children who exercised also showed increased activity in an area of the brain responsible for executive function, suggesting an improved ability to make decisions in general.

Exercising 40 minutes a day for three months improved intelligence scores by nearly four points. And while the study was performed on overweight children, the researchers believe exercise would do the same for normal-weight children.

The exercise was basically outdoor fun and games, including running games, hula hoops and rope jumping. Exercising 40 minutes a day for three months improved intelligence scores by nearly four points. Twenty minutes a day led to a smaller improvement. And while the study was performed on overweight children, the researchers believe exercise would do the same for normal-weight children.

The study was of 171 sedentary overweight children aged 7-11. They were split into three groups. Two groups exercised after school for 13 weeks, one group for 20 minutes a day, the other for 40 minutes. The exercise was basically outdoor fun, kids running around and being kids. The third group did not exercise after school.

The children were tested before and after the 13 week program, using the Cognitive Assessment System and the Woodcock-Johnson Tests of Achievement III. These tests measure both academic skills and cognitive abilities such as planning. Some of the children also had a brain scan (fMRI) taken before and after completing the exercise program.

Forty minutes of exercise a day translated into a 3.8 point test score improvement. Scans of those who exercised showed an increased activity in the brain's prefrontal cortex, an area associated with executive function which includes planning and decision making and understanding the difference between appropriate and inappropriate behavior.

Improved executive function implies a better ability to make all life decisions, not just those involving school.

The researchers hope these results will make clear to educators the importance of physical activity and help ensure that vigorous physical activity is a standard part of the school day.

An article on the study was published in the January 2011 issue of Health Psychology.