BOSTON — Andover school students have traded in potato chips for whole-grain pretzels, hummus with pita bread, and fruit smoothies.

In Lawrence, schools have banned chocolate milk and sugary drinks, and now reach out to farms for fresh produce and fruit. High school students grow tomatoes, hot peppers and eggplants in gardens near the school.

Prodded by stringent state and federal standards, cafeterias in Massachusetts schools are serving more nutritious meals, state officials said, despite the challenges of getting kids to eat healthier foods and the increased cost.

“School meals aren’t what they used to be,” said Rob Leshin, acting director of the office of food nutrition at the state Department of Elementary and Secondary Education. “We’ve moved past hot dogs and potato puffs to salad bars, fruit and vegetables.”

The standards are part of the Healthy, Hunger-Free Kids Act of 2010, championed by first lady Michelle Obama. The legislation made sweeping changes to meals served in schools that get federal funding. The rules prescribe ingredients in foods such as pasta and cheese sandwiches, limit calories in each serving, and dictate what kind of milk is served.

They also require that meals include at least one serving of fruits and vegetables.

Gail Koutroubas, director of food and nutrition services for Andover’s schools, said the district started moving toward a healthier menu several years before the new standards were introduced, removing deep-fryers from its kitchens.

“Once we took out the fryolators, we started to change the menu by introducing grains, fresh fruits and vegetables,” she said.

Snack bars and vending machines selling sugary drinks and junk food were pulled from every cafeteria, except in the high school. The district also added whole-grain spaghetti, breads and pizza to its menus. Even the once-a-month pizza from Domino’s is now prepared specially based on the new standards.

“Like most things, it took time and persistence,” Koutroubas said. “Kids usually have to see things a few times before they’ll eat it.”

The state’s 402 public schools serve more than 500,000 lunches a day — or more than 90 million a year — state education officials said.

“Collectively, they are the state’s largest restaurant,” Leshin said. “And they’re operating with limited resources, under the strictest federal and state guidelines, and serving some of the pickiest customers.”

Lawrence is one of 171 school districts participating in the state’s farm-to-school program, which allows cafeterias to buy produce and fruit from farmers using federal and state dollars. Lawrence schools contract with several local producers including Brooksby Farm.

“We’re constantly trying to improve the menu while giving the kids healthy foods they will eat,” said Gary Watts, the district’s director of nutritional services.

But switching to better foods drives up costs in many cases. The state requires local school lunch programs to be self-sustaining.

“There’s a tremendous cost because unhealthy foods are cheaper,” Koutroubas said. “We’ve gone through a few rough patches when our lunch participation declined and the revenues were not where we wanted them, but we’re 100 percent self-supporting now.”

Leshin said the state and federal government offer grants to offset the costs of healthier foods. The Defense Department also gives schools access to surplus fruits and vegetables grown for military bases.

“They’re getting excellent fruits and vegetables at no cost,” he said. “So as you can imagine the demand exceeds the supply.”

That’s in addition to the U.S. Department of Agriculture’s longtime subsidy for school cafeterias. Federal reimbursements this year are $3.07 per meal for students who are income-eligible for free lunches; $2.67 for those who qualify for a reduced-price lunch; and 29 cents for all others sold.

Nationally more than 98 percent of schools are implementing the nutrition standards, according to the USDA. School leaders said the healthier choices have also played a role in a growing number of states and cities where childhood obesity rates are declining, including in New Hampshire and Massachusetts.

A study published earlier this year in the journal JAMA Pediatrics said the standards have had a “substantial impact” on the quality of food.

In some cases, school have made exceptions to the rules. In 2012, Gov. Deval Patrick signed a bill exempting concession stands, school fundraisers and other school events.

And lagging sales in school cafeterias show not everyone is buying into the healthier meals.

Lunch participation nationally has dropped from 31.8 million students in fiscal year 2011 to 30.4 million in fiscal 2015, according to the USDA.

In Massachusetts, participation dropped 26,921 students during those years. New Hampshire’s participation fell by 19,053 during that time.

Leshin said the trend appears to be leveling off — and in school districts such as Salem, Mass., and Andover, more students are buying lunch.

“It’s definitely rebounding,” he said. “Some districts are even turning a profit.”

A recent survey of 60 school districts by the state Department of Public Health found that cafeterias were meeting, and in some cases exceeding, nutritional standards.

“A number of the school officials we spoke with noted that students often received the most nutritious meal of the day at school,” a DPH report stated.

Still, groups such as the School Nutrition Association say the changes are still driving up costs for schools and have resulted in more food waste from students who don’t eat their fruits and vegetables.

“School districts are being forced to financially subsidize meals at the expense of educational programs,” the association wrote in a letter to congressional lawmakers last year.

The group said the federal requirements tacked on 10 cents to the cost of a lunch, on average, and 27 cents to the cost of a school breakfast.

School districts were only given an additional 6 cents per lunch and no extra for breakfasts.

Koutroubas said she understands criticism over costs and regulation, but the changes were necessary.

“We needed to do this, because a lot of people were simply not doing right by the children,” she said. “Selling cookies and candy bars is not what was intended for the school lunch program.”

Christian Wade covers the Massachusetts Statehouse for the North of Boston Media Group’s newspapers and websites. Reach him at cwade@cnhi.com.