But, she hastily added, she gets the small bag.

Crystal was one of 1,349 Philadelphia elementary school pupils who participated in a two-year experimental program to provide healthy alternatives to such snacks as potato chips in their schools.

And if nothing else, Crystal and the other students are now more aware of what is healthy and what is not.

Crystal and Gabrielle Hudnell, 9, both students at the Fairhill School, Somerset Street near 6th in North Philadelphia, were asked what they thought of the program.

"My mom buys healthy foods now," said Gabrielle. "We have three packs of strawberries, grapes and bananas."

There was mostly good news when results of the study - which replaced sodas with fruit juice, scaled back snacks and banished candy at five city elementary schools - were announced today.

The number of kids who got fat was half the number of kids who got fat in schools that weren't in the program, researchers said.

Unfortunately, there were still plenty of overweight kids in the schools - over 7 percent of them became overweight compared to the 15 percent in the schools that didn't make changes.

"That signals to me that we have lots more work to do," said Gary Foster, director of the Center for Obesity Research and Education at Temple University.

He was the lead author of the study, the results of which are being published today in the April issue of Pediatrics.

The Philadelphia study put to the test a program developed by the Food Trust, a nonprofit that works to improve access to affordable, healthy food.

For the study, changes were made to the food in vending machines or the cafeteria. Juice, water and low-fat milk replaced sodas. Snacks had to meet limits for fat, salt and sugar.

Students who ate healthy snacks got raffle tickets to win prizes ranging from bikes to jump ropes.

In addition, students, teachers and parents were taught good eating habits and how to get the children to make good choices.

Of the results, Foster said, "It's a really dramatic effect from a public-health point of view."

Joan Nachmani, the school district's director of nutrition education and one of the researchers, said such studies help people "wake up and realize it can be done on a larger scale."

"We found that when you give children healthy choices, they pick them," said Grace McKinley, school nurse at one of the test schools, the Francis Hopkinson School, at L Street near Luzerne in Juniata Park .

Lessons on good nutrition were reinforced by such devices as using food labels to help teach fractions.

Parents were enlisted. A fundraiser that normally features baked goods substituted fruit salad.

Sandy Sherman, the Food Trust's director of nutrition research, said that the children were also urged to exercise at activity stations during recess.

They were measured and weighed periodically and surveyed about their knowledge of food and exercise.

After two years, besides fewer new overweight children, the overall number of overweight students at the test schools dropped 10 to 15 percent.

At the no-change schools, the number of overweight children rose a quarter to 20 percent.

Sherman said that the researchers found that students spend about $2 a day buying snacks that average 600 calories.

Mike Prelip, of the UCLA School of Public Health, said that the study design was rigorous and that the results were interesting. But he added, "One intervention usually won't work for everyone. That's why it's good to have multiple approaches."

Temple University and the Food Trust are now working with local grocery stores to get them to offer more cut-up fruits and vegetables, water and single-service snacks. *