New numbers from the federal government find only 25 percent of children ages 12 to 15 get the recommended amount of daily physical activity.
The study found half the children exercised an hour a day five days a week.
With more than a third of children and adolescents overweight or obese in the U.S., guidelines say kids should be getting 60 minutes of exercise a day.
Physical education teacher John DeMatteo says the key is to find the right activity for each child.
"The kids have to have fun," he says. "If they're not going to have fun we are going to lose them to video games and television and computers."
Basketball was the most popular sport among active boys.
Running was the most popular sport among active girls.