They winced while their blood was drawn and fidgeted as the blood pressure cuff tightened. But the sixth-graders were excited about becoming test subjects in a nationwide diabetes study, if only to score the $50 gift card being offered.

For researchers, the payoff won't come for nearly three years. But it'll be worth the wait if the study at dozens of middle schools concludes schools can help lower the risk of Type 2 diabetes in children by offering healthy choices in the cafeteria and revamping gym class.

"We want to know if there's some structural way to prevent diabetes rather than to just tell kids, 'Eat the right thing,"' said Gary Foster, the study's chairman and director of the Center for Obesity Research and Education at the Temple University School of Medicine.

The so-called HEALTHY study, sponsored by the National Institutes of Health, will follow sixth-graders over a 2 1/2-year period with results expected in 2009. Students in North Carolina, Texas, California, Pennsylvania and Oregon will participate.

One group of students will be exposed to the kinds of food and gym classes available in most U.S. middle schools, and a second group will get healthier cafeteria food, more rigorous gym classes and advice on healthy behaviors.

Last week, researchers from the University of North Carolina at Chapel Hill helped coordinate initial health screenings at Overhills Middle School in Spring Lake, about an hour south of Raleigh.

A few dozen sixth-graders went to the school's auditorium to get their blood pressure taken, weight, height and waist size measured and blood drawn to check levels of glucose, insulin and lipids. At the end of their eighth grade year, they'll go through a similar screening.

Overhills is one of the schools trying the healthier options.

"We're asking schools to make some pretty dramatic changes to the way they do business," Foster said.

The study is targeting schools where at least half the students are minorities, and at least half qualify for free or reduced-price lunches. Past studies have shown that minorities and those with less access to health care are at a higher risk for Type 2 diabetes, which is linked to obesity.

"I'm worried about it," said Brittani Jefferson, 11. Several people in her family have diabetes, so she fears she's at risk.

She said she tries to eat right and exercise, but she likes snacking on things like popcorn and chocolate.

"I went home and talked to my mom, and we both thought it was a good idea," Brittani said as she waited to get her blood drawn during the screening. "It pretty much runs in my dad's family, so I could get it."

Rose Cooper, the principal at Overhills, said parents will have access to a report on the health screenings, which can be valuable for families that don't have health insurance. It also helps that the students get a $50 Wal-Mart gift card for participating, she said.

"They're excited, because they feel important," she said. "They're not only doing something for their community, but also for students across the nation."

In recent years, it's been challenging for public health advocates to get schools to spend more time talking about health and put their students in gym class longer and more often, said Joanne Harrell, a nursing professor at UNC Chapel Hill and lead investigator of the North Carolina portion of the study.

"It's been a lot harder because of the emphasis on and the need for academic achievement," Harrell said, adding that the HEALTHY study will also track students' attendance and academic achievement.

Alice Ammerman, a professor at the UNC Chapel Hill School of Public Health, said current research on diabetes and obesity in children has focused on changes to their environment, such as the school setting.

"I think these broader environmental and policy changes in schools are going to be the best way to impact a variety of kids, rather than just targeting individual kids who are higher-risk," said Ammerman, who is not a part of the federal study.

The challenge for health advocates is getting schools to adopt changes that won't require too much time or too many resources, Foster said.

"We have to develop programs that fit into the school culture. We can't distract from their core academic mission," he said.