The group of kids walking or biking to school concentrated better than those driven to school or taking public transport, and the effect lasted throughout the morning hours. On average, active students scored 8.2 - 8.4 on a concentration test (of a possible 10) while non-active students scored an average of 7.6 - 7.8. This was more than the concentration difference shown between students who did eat breakfast (8 - 8.15) and those who didn't (8.1 - 8.25).
Unfortunately, in the Nordic nations and in the U.S., the trend for how children get to school is going in the opposite direction - more children are getting driven to school than ever before. Parents perceive walking and biking to be dangerous, while actually things have gotten safer for cyclists in many, many places, and overall fatalities are trending downward.
Of course, correlation is not causality, so it can't be said with certainty that riding a bike to school will make you smarter, anymore than it can be said that driving in cars will make you fat. With biking, there are so many other benefits, real and perceived, that it certainly seems worth a try to get parents off the driving-the-kids-to-school frenzy.
Via: Ecoprofil (Swedish)