The course includes a number of components, including exercise, nutrition and learning how to cook healthily.
Many of the participants - who come from around the country - had grown up loving certain kinds of foods, he said. The course helped change attitudes when it came to eating those foods.
"We get kids coming in who love their chop suey and spaghetti bolognese and all that stuff. But they've only eaten it a certain way. We teach them how to cook things in a healthier way and it's teaching parents, too."
The former rugby league star and professional boxer said the courses were something he had always wanted to do, given he also faced problems with his weight as achild.
"I was really overweight when I was a little kid. But then I got into karate and other sports and just went from there. I'm really passionate about this cause because I want to see kids doing better for themselves."
Betham's sister and chief executive of Steps For Life, Chante Betham-Spencer, said those who signed up for the course did so for a variety of reasons.
Many youngsters admitted they did not want to die early, while others simply wanted to play a game of touch rugby with their mates and not get puffed out.
"For other kids, they just want to walk into a mall and be able to buy something that fits."
On the web: stepsforlife.co.nz/
