Lead author Martha Kubik, an associate professor at the University of Minnesota, acknowledged her research doesn't prove that such food practices contribute to adolescent obesity, but there does seem to be a connection.

"I think we all have to step back and look at what we're doing to contribute to practices that might not support children developing healthy dietary behavior," she said.

Kids Are Actually Eating Apples and Oranges

Her study's results make sense to Kevin Miller, principal of Fair Haven Middle School, which banned bake sales and went junk-food-free as part of a districtwide program in New Haven, Conn. Miller doesn't allow vending machines, and his cafeteria promotes healthy food.

Kids are actually eating apples and oranges instead of throwing them away. And because there aren't any candy wrappers around, he said, "our hallways are impeccable."

There was vindication, too, for Texas Agriculture Commissioner Susan Combs, who responded to rising childhood obesity by leading a statewide crackdown on junk food in schools last year. The Texas effort specifically targeted treats and bake sales, along with vending machines.

Combs said she ran up against a "very deeply entrenched culture," even among elementary school teachers, who often used candy as rewards. She said she was horrified by an e-mail from one teacher who said she couldn't imagine not using candy an incentive. Equally entrenched, she said, was the attitude that food sales were the only effective fund-raisers.

"When you have the authority figures such as teachers, principals and parents pushing food which is high in calories and low in value day after day, hour after hour in schools, it's absolutely devastating to trying to run a healthy nutrition policy," Combs said.

Alternative Fund-Raising Strategies

In Connecticut, Miller said he didn't get much resistance. He talked over alternative fund-raising strategies with the Parent Teacher Organization -- options such as concerts and car washes.

"If you only know bake sales, that's all you think you can do," he said.

Since food rewards are banned, teachers give students pencils and other "tools of academia" bearing the school logo.

The Minnesota study looked at whether the schools had seven specific "food practices" that would allow students access to food outside of normal meal programs. Sixty-nine percent allowed the use of food for incentives and 56 percent allowed food in classroom fund-raising.

They found that the body-mass index of students -- a calculation based on weight and height -- was 10 percent higher for each additional food practice allowed in their school. The study was published Monday in the Archives of Pediatrics and Adolescent Medicine, a publication of the American Medical Association.