Over the last two decades, obesity rates have doubled in children and tripled in teen-agers.
One in seven young people is now obese.
"We have seen almost an explosion of the number of children approaching or seeking help with problems with weight," said Dr. Ovidio Bermudez, a child obesity expert.
School is where millions of kids learn their nutritional ABC's -- All Bad Choices, reports CBS News Correspondent Mark Strassmann.
Soda, candy and junky snacks, all sold from machines right on school grounds.
Near Atlanta, high school senior Toshe Satake practically lives off soda: "Probably one in the morning, one at lunch and one after school. So probably about three."
A recent national survey showed vending machines in 43 percent of elementary schools, 74 percent of middle schools, and 98 percent of high schools.
"We realize we're in a crisis situation," said health teacher Jacqueline Domac, who led the drive at California's Venice High to ban sales of soda.
"This is a captive audience that we have here. And it's not fair to push all these unhealthy things upon our students," she said.
Now the school sells only water, juice and healthier choices.
"I've cut down on soda. Totally cut down on soda," said Venice High freshman Salsabil Elmagr.
But many principals, including Wayne Parker, admit that it's the schools themselves that are really bingeing on snacks and sodas.
"It's bought uniforms for all the sports. It's provided for us to pay for officials and other activities for out athletics," Parker said. "These machines make big money, at a time when many states face a budget crisis. The overriding health issue is financial."
Said health teacher Domac: "The burden should not be on our students, and have them suffer with their health, because we can't manage our money."
To the soda industry, the real issue with kids and fatness is fitness, not a can of Coke.
"We think we have an societal issue that goes beyond two quarters going into a vending machine," said Raymond Thomasson of the Tennessee Soft Drink Association.
And at Venice High, some students scoff at the ban on school-sold soda.
"You're not teaching the kids to make better choices. All you're doing is telling them, while you're at school, you have no choice. You have to eat healthier," said Venice High junior Alex Miller.
But often, not in the school cafeteria, where for lunch, students can buy gooey pizza or munch on nachos and cheese.
More grease for critics complaining that America's schools keep selling out the health of America's kids.
Part 2: Balanced Nutrition, Better Behaved Kids