NEW YORK - Khalil Colon was sweaty but smiling after 25 jumping jacks and 20 laps around the school gym.

A year ago, the 9-year-old said, running made him feel “like I'm about to drop on the middle of the floor.”

“But now I can run 20 laps and I'm not even tired,” said Khalil.

Twenty laps is the magic number because it's a mile. Khalil is one of 20,000 New York City schoolchildren enrolled in the Mighty Milers, a program run by the New York Road Runners Foundation that aims to get kids up and running.

The program, which targets childhood obesity, is in more than 100 New York City schools plus 20 schools in other states and 20 in Cape Town, South Africa, where a non-governmental organization became interested.

The children earn prizes like medals and certificates each time they notch 26 miles - a marathon - and they can track their progress on personal Web pages.

The running club is best known for putting on the New York City Marathon, which draws world-class runners and hobbyists alike on the annual race through the five boroughs. But foundation Executive Director Cliff Sperber said the purpose of the Mighty Milers isn't to raise a new generation of marathoners.

“The purpose is to give back to the community,” he said.

At this year's Nov. 4th marathon, 1,200 runners will collect fundraising pledges for the Mighty Milers and the foundation's other youth programs.

In New York City, a 2003 Health Department survey found that only 53 percent of public elementary school students were at a healthy weight.

Overweight children are more likely than their slimmer peers to become overweight or obese adults and to develop health problems including heart disease and diabetes.

Principal Israel Soto said Public School 57 in East Harlem is addressing the obesity challenge through a range of measures including a gym for the staff and nutrition classes for parents.

Mighty Milers fits in with his goal of nurturing healthy bodies and healthy minds.

“The research is very clear that when children are healthy, when you provide opportunities for them to get healthy, it raises their achievement level,” he said.

Sperber said Mighty Milers costs just $50 per child per year, including T-shirts, prizes and training for the physical education teachers at participating schools.

At P.S. 57 this past week, physical education teacher Maisha Cadet-Duval had 28 fourth-graders counting their laps as they ran or walked around the gym.

When they had completed 20, they jumped rope and then got out mats for sit-ups.

The class ended with a spirited game of beach-ball volleyball.

Cadet-Duval said the students are more fit thanks to Mighty Milers.

“Last year when we first started the program, after the second lap they were done,” she said.

Nine-year-old Cierra Agosto said she loves the program.

“When we didn't have Mighty Milers, we didn't have so many activities,” she said. “We never got to do push-ups and sit-ups before.”

Cierra boasted that her friend Katherine Rojas, also 9, is the fastest runner in the class; she can do a lap in 15 seconds.

“That makes me feel good about myself,” said Katherine, petite and ponytailed. “And it helps you get muscles.”