They're trying at Upper Darby High School. They really are.

As 3,800 students stream through the cafeteria in four shifts each school day, the well-meaning lunch ladies try to steer them to a more healthful diet - to drink milk and an ersatz fruit slush instead of sweetened iced tea, to try the low-fat turkey sandwich on wheat bread instead of white. There's a chicken cheesesteak offered alongside the red-meat variety, and the kids have to stand in a separate line to buy ice cream and chips.

But there's not a piece of fresh fruit in sight. The only fresh vegetable besides lettuce is sliced tomato. And the meatball sandwiches, Italian hoagies, pepperoni pizza by the slice, pasta Alfredo, french fries and irresistibly aromatic freshly made cookies are too strong a temptation. During an entire lunch period one day last week, when hundreds and hundreds of meals were served, I saw only 14 kids buying what passed for a green vegetable, a Caesar salad.

You can only imagine the pile of leftovers if lentils and brown rice were served.

Upper Darby High's cafeteria - bright, clean, surprisingly orderly, given the waves of teenagers passing through it each day - looks like a mall food court because that's what eating has become for most Americans: brown, packaged, quickly consumed. This is, of course, one reason why half of all Americans are overweight or obese, and childhood obesity is increasing at alarming rates. (The other reason is that we're as sedentary as a turtle in sunshine.)

But the 53 million children who eat at school every day are a captive audience, and the nation's school-lunch program is considered the largest feeding program in the world. With all we know about good nutrition, brown still rules. What about food that is green, yellow, orange, red, purple?

"The way lunches are being served comes with fast-food values," says Alice Waters, the renowned chef and restaurateur, who is turning her considerable passion for food toward improving what's served in the nation's public schools.

"Kids are taught it's OK to eat in a great hurry, the same way every day. There's no value attached to food. It should be cheap, and the people who make it and serve it don't need to be paid well," she says. "Food is disconnected from the seasons. And you're not supposed to ask where it came from."

Waters can afford to be idealistic - after all, she lives in Berkeley, Calif., where liberal notions and plentiful, fresh produce are grown in equal measure. But she's not to be dismissed. When she opened her trendsetting, award-winning Chez Panisse restaurant 30 years ago, organic cooking and seasonal menus were scoffed at, too.

Now she's negotiating with the Berkeley public schools to run some or all of its food service and create an interactive program with gardening, classroom instruction and hands-on cooking. She cites research by Antonia Demas at Cornell University showing that if children had a positive introduction to healthful foods, they would eat things their parents swore they'd never touch.

"Kale! Radicchio! They've never been offered this stuff," says Waters. "But if they grow it, plan the menu, cook it, serve it to their friends, they eat it."

Sure, this is a far cry from the reality of school lunchroom life, where the sweet, slushy drink called Vita-Pup, made mostly of flavored grape juice, is allowed to pass for "fruit." But decades after ketchup was declared a vegetable, the tide may finally be turning. Just last month, the Los Angeles school district, concerned that about 40 percent of its students are obese, voted unanimously to ban the sale of soft drinks at all of its sites.

Demas, president of the nonprofit, educational Food Studies Institute, is in negotiations with Philadelphia officials to train teachers in her food-based curriculum, which she says is proven to improve nutrition and children's behavior. Better-fed children are more attentive in class and less likely to fall asleep when the sugar high wears off.

"The biggest obstacle," she says, "is getting people to realize that food is important and has an impact on learning."

Children, after all, are only adopting the fast-food values of their parents. For proof, look no further than the road leading to Upper Darby High School. They try hard at the school, they really do, but the road to their good intentions is paved with McDonald's, Dairy Queen, Dunkin' Donuts. Need I say more?