In a third-grade classroom at Glen Lake Elementary School in Minnetonka on Friday, children in brightly colored tissue paper crowns moved through a do-it-yourself trail mix line, choosing from crackers, popcorn, dried fruit and other healthful treats.

Teacher Kate Humphrey, in a rickrack-festooned party apron, directed one boy's attention to a bowl of crimson dried fruit.

"Have you ever had Craisins?" she asked, smiling as she popped one into his bowl. "Today you get to try one."

Many classrooms across the Twin Cities are changing their relationships with treats. Nutrition and health experts cite many reasons, namely childhood obesity and classroom management, for limiting outside food from the classroom. If treats are served, they often serve double duty, as part of a lesson on nutrition, math or culture. For Glen Lake third-graders, the last Friday of the month is Healthy Snack Friday. Often, students make their own snacks. They measure, add and try to multiply recipes to serve a crowd.

"People have to understand, more than anything, the gravity of where our children's health is at," said Barb Mechura, Hopkins Schools' director of student nutrition services. "Really, food has been woven into so many parts of the school environment and into the fabric of what schools are, and we have to unravel that and say, what's reasonable?"

Nationally, about 17 percent of people under age 20 are obese, according to recent statistics from the Centers for Disease Control and Prevention. The rate has tripled since 1980, though it has leveled off in recent years. The federal agency also estimates that as many as 6 percent of children have food allergies that put cow's milk, eggs, nuts or wheat off-limits.

The Minnesota Department of Education doesn't track how schools approach treats and parties, said Debra Lukkonen, the state's supervisor of school nutrition programs.

But she said she knows schools are moving toward healthier eating outside of the lunchroom. Anoka-Hennepin's nutrition services will provide more healthful snacks -- veggies and dip, "ants on a log" and popcorn. St. Paul limits food celebrations to once a month.

Nutrition experts said special days could be marked with a small toy, extra recess time, a game, a craft, or a crown or button for a birthday child.

School nutrition directors noted that as our relationship with food and exercise has changed, so, too, must we change how we use them. In a class of 30 students, a 36-week school year can mean a birthday a week, in addition to other celebrations.

"If there are too many celebrations happening, or students are receiving too many treats, that can lead to issues of excess calories, and not necessarily the ones that are the most nutritious for kids," said Jean Ronnei, director of Nutrition Services for St. Paul Public Schools. "We look toward celebrating things, not necessarily focused on treats, to limit those and find other ways to celebrate."

In Anoka-Hennepin, efforts to find and market ideas for healthier school celebrations were funded by a Statewide Health Improvement Program (SHIP) grant. The party-catering service that launched this year was part of that.

"We haven't prohibited anybody from sending [cookies and cupcakes] from home," said Patty Dueno, the district's assistant director for child nutrition programs. "This is just another option for parents, so if they think it's important for children to have a different kind of snack that sets an example for their children and their children's friends, this is another option for them."

In some cases, limiting snacks helps teachers and parents of kids with allergies exercise a little bit of control over what comes into the classroom.

"It's a statewide issue." said Mary Heiman, president of the School Nurse Organization of Minnesota. "It's very difficult for us to say we can be peanut free or allergy free, allergy safe. ... It needs to be forefront on the classroom teacher's mind. That's a lot of responsibility, so why not take that away as best we can and not serve snacks?"

Rockford Area Schools parent Kari Heitke, of Corcoran, said she has mixed feelings about a general departure from unhealthy but yummy treats at school.

"In the United States, food is a celebratory thing, and if you want to have a birthday, I think you should be able to choose when you want to," she said. "It should be left up to the individual."

Still, she said, her experience as a substitute teacher colors her opinions.

"You see the big cupcakes or the big boxes of doughnuts, and as a teacher you think, 'oh no,'" she said "Kids do go crazy when they eat a full cupcake."

At Glen Lake, parents still may send in cupcakes and cookies for birthdays, but kids can tell the difference between healthy and unhealthy snacks.

"It's changed dramatically," said Julie Burke, another third- grade teacher at Glen Lake.

Between Humphrey's and Burke's classes, there was a girl with diabetes and a boy with food allergies. Their snacks had to be checked by the nurse and cross-referenced with a list from home.

"There's so much," Burke said. "When I started 30 years ago, you didn't even think about it."

Maria Elena Baca • 612-673-4409