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:
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.
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."
Children ages 8 to 12 see an average of 21 television ads each day for candy, snacks, cereal and fast food - more than 7,600 a year, according to a recent Kaiser Family Foundation study. Not one of the 8,854 ads reviewed promoted fruits or vegetables.
There was one ad for healthy foods for every 50 for other foods.
Children may be the best sources to explain why lessons about nutrition don't sink in.
"I think it's because they like it so much, because like, I don't know if you've seen the new hot Cheetos that are like puffs? Oh my God, they're so good. Like everyone at the school has them and they're so good," said Ani Avanessian, 14, of Panorama City.
Her classmate George Rico, a 13-year-old whose mother is a manager at a McDonald's, said he loves his nutrition class. But does it affect what he puts in his mouth?
"Well, no, but it makes me think about what I eat," he said. "I think kids don't change because they've been eating it for so long they're just accustomed to eating that way."
Their teacher, Jenkins, offers fact-filled and engaging nutrition lessons as part of a $7 million USDA program which reaches about 388,000 students a year in the Los Angeles Unified School District.
The most recent evaluation of the 8-year-old program was disheartening: no difference in the amount of fruits and vegetables eaten by kids participating in the program and those who weren't. Teachers who spent more hours on nutrition education had no greater impact than those who didn't. And parent behavior didn't change either.
"It's true, it didn't change what they actually eat. But the program really made a difference in how kids were feeling about fruits and vegetables. They really had a more positive attitude toward fruits and vegetables," said Dr. Mike Prelip, a UCLA researcher who headed up the evaluation.
Kate Houston, deputy under secretary of the USDA's Food, Nutrition and Consumer Services, oversees most federal funds, $696 million this year, spent on childhood nutrition education in this country. Funding has steadily increased in recent years, up from $535 million in 2003. Houston insists the programs are successful.
"I think the question here is how are we measuring success and there are certainly many ways in which you can do so and the ways in which we've been able to measure have shown success," she said.
But isn't the goal of these programs to change the way kids eat?
"Absolutely that's the goal," she said.
And they're successfully reaching that goal?
"We're finding success in things in which we have been able to measure, which are more related to knowledge and skill. It is more difficult for us to identify success in changing children's eating patterns."
When asked about the many studies that don't show improvement, Houston asked for copies of the research. And she said the USDA doesn't have the resources to undertake "long term, controlled, medical modeled studies" necessary to determine the impact of its programs.
Doctors like Tom Robinson, who directs the Center for Healthy Weight at Lucile Packard Children's Hospital at Stanford University, said those studies aren't needed. The research has already shown they don't work.
"I think the money could be better spent on programs that are more behaviorally oriented, as opposed to those that are educationally oriented, or studies that just describe the problem over and over again," he said.
There may be pieces of solutions found in limited studies currently being tested around the country. In some situations, obese and overweight children can lose weight and get healthy through rigorous hospital and clinic-based interventions that involve regular check-ins, family involvement, scheduled exercise and nutrition education.
School programs that increase physical activity are also more likely to have an impact than nutrition education.
This spring the Robert Wood Johnson Foundation announced plans to spend $500 million over the next five years to reverse the trend of childhood obesity. It will fund programs that bring supermarkets into poor neighborhoods, studies that measure the weight of children who exercise more at school, meetings of advocates who are seeking to restrict junk food ads.
One thing it won't fund: projects that only provide school nutrition education.