When 14-year-old Benjamin Ring walks his dog, Jasper, he earns 200 points. When he runs a mile, he gets 500 points. If he hikes with his family or walks to school, he racks up "pointz" that he can redeem for prizes.

"It's like a real-life upgrade," the eighth-grader from Piedmont, California, said about the game Zamzee.

So far, the bespectacled teenager has 47,074 pointz which he has redeemed for Legos and $150 worth of Best Buy gift cards.

Benjamin, a lean and lanky adolescent with bowl-cut hair, is not on a weight-loss program. But he readily says the game has made him more invested in physical activity.

"It made me more interested in exercise because I got money," he said. "I wanted to walk the dog and run as much as I could for PE."

Gaming and screen time have been blamed for contributing to the childhood obesity epidemic, with about one out of three U.S. kids overweight or obese. But there is growing interest in using the addictive, entertainment value of gaming to promote health -- for kids and adults.

"The thinking was, how can we use games for good?" said Fred Dillon, director of product development at Hopelab/Zamzee. "It's obvious kids really like games. Is there a way to take things that kids are already doing and power them for good and health?"

Zamzee tries to instill behavior changes by rewarding exercise and teaching healthy habits. It blends the real world and online experience, because when Benjamin moves in the real world, that movement racks up points for his avatar and allows him to compete against his peers for the most physical activity.

An accelerometer clipped to Benjamin's jeans monitors his moderate to vigorous activity. When he loads data from this device through a USB port into his computer, it shows how much activity he has had since his last login. He can compare how he's doing with other kids. He ranks 53rd among about 3,000 competitors in accumulated lifetime points.

Zamzee, which is expected to become available to the public this fall, is the product of a nonprofit called Hopelab, created by Pam Omidyar. Omidyar, who is married to eBay founder Pierre Omidyar, first used video gaming to help young cancer patients. Hopelab created the 2005 game Re-Mission, in which a heroine travels through the bodies of fictional patients to destroy cancer cells. The video game helped young patients stick with their treatments and improved their cancer knowledge, according to a study published in the journal Pediatrics.

Then the group turned to the problem of childhood obesity. With Zamzee, the idea is to get the kids moving.

"We're hoping that this is igniting a desire to move for the rest of their lives," said Richard Tate, Hopelab's vice president of communications and marketing.

Health researchers want to reach kids and tweens like Benjamin and help them form healthier habits. But competition for their attention is fierce.

Benjamin would rather sit in front of his computer building shelters and contraptions to keep out the monsters on the game, Minecraft, than exercise outside.

"I don't like sports," he said, with a shrug.

Benjamin was asked to participate in the testing phase of Zamzee through a neighbor involved with the project.

His dad, Jonathon Ring said, "I was secretly hoping that it might motivate him to get outside, with his friends and go to the park instead of just sitting on his butt."

"Which I do," Benjamin chimed in.

"I definitely like hiking," he said. "It's one of my favorite things. I think it came out of this."

His dad agrees. Since Benjamin's introduction to Zamzee four years ago, Ring has noticed changes in his son's activity.