But an Associated Press review of scientific studies examining 57 such programs found mostly failure. Just four showed any real success in changing the way kids eat _ or any promise as weapons against the growing epidemic of childhood obesity.

"Any person looking at the published literature about these programs would have to conclude that they are generally not working," said Dr. Tom Baranowski, a pediatrics professor at Houston's Baylor College of Medicine who studies behavioral nutrition.

The results have been disappointing, to say the least:

_Last year a major federal pilot program offering free fruits and vegetables to school children showed fifth graders became less willing to eat them than they had been at the start. Apparently they didn't like the taste.

_In Pennsylvania, researchers went so far as to give prizes to school children who ate fruits and vegetables. That worked while the prizes were offered, but when the researchers came back seven months later the kids had reverted to their original eating habits: soda and chips.

_In studies where children tell researchers they are eating better or exercising more, there is usually no change in blood pressure, body size or cholesterol measures; they want to eat better, they might even think they are, but they're not.

The studies don't tell Leticia Jenkins anything she doesn't know. She's one of the bravest teachers in America _ not because she gave her seventh and eighth graders 30 sharp knives to chop tomatoes, onions, jalapenos and limes for a lesson on salsa and nutrition, but because she understands the futility of what she is trying to do.

"Oh, it's so hard, because at the end of the day sometimes I take a moment, I think gosh, I did all this and we still see them across the street picking up the doughnuts and the coffee drinks," she said.

Nationally, obesity rates have nearly quintupled among 6- to 11-year-olds and tripled among teens and children ages 2 to 5 since the 1970s, according to the Centers for Disease Control. The medical consequences of obesity in the U.S. _ diabetes, high blood pressure, even orthopedic problems _ cost an estimated $100 billion a year. Kentucky cardiologist Dr. James W. Holsinger Jr., nominated as the next surgeon general, says fighting childhood obesity is his top priority.

The challenges to changing the way children eat are as numerous as the factors that have prompted the obesity epidemic in the first place.

The forces that make kids fat "are really strong and hard to fight with just a program in school," said Dr. Philip Zeitler, a pediatric endocrinologist and researcher who sees "a steady stream" of obese children struggling with diabetes and other potentially fatal medical problems at The Children's Hospital in Denver.

What does he tell them?

"Oh God, I haven't figured out anything that I know is going to work," he said. "I'm not aware of any medical model that is very successful in helping these kids. Sure, we try to help them, but I can't take credit for the ones who do manage to change."

The obstacles are daunting:

PARENTS. Experts agree that although most funding targets schools, parents have the greatest influence, even a biological influence, over what their children will eat. Zeitler says when children slim down, it's because "their families get religion about this and figure out what needs to happen."

But often, they don't.

"If the mother is eating Cheetos and white bread, the fetus will be born with those taste buds. If the mother is eating carrots and oatmeal the child will be born with those taste buds," said Dr. Robert Trevino of the Social and Health Research Center in San Antonio.

Most kids learn what tastes good and what tastes nasty by their 10th birthdays.

"If we don't reach a child before they get to puberty, it's going to be very tough, very difficult, to change their eating behavior," said Trevino.

POVERTY. Poorer kids are especially at risk, because unhealthy food is cheaper and more easily available than healthy food. Parents are often working, leaving children unsupervised to get their own snacks. Low-income neighborhoods have fewer good supermarkets with fresh produce.

"If Mom can't find tomatoes in her local grocery store, nothing is going to change," said Zeitler.

Meanwhile, it's harder for children to exercise on their own. Parks often aren't safe and sports teams cost money.

"Calorie burning has become the province of the wealthy," said Zeitler. "I fear that what we're going to see is a divergence of healthy people and unhealthy people. Basically, like everything else, it costs money to be healthy."