WASHINGTON — Harder times and higher fuel prices are following kids back to school this fall.

Children will walk farther to the bus stop, pay more for lunch, study from old textbooks, even wear last year’s clothes. Field trips? Forget about it.

This year, it could cost nearly twice as much to fuel the yellow buses that rumble to school each morning. If you think it’s expensive to fill up a sport utility vehicle, try topping off a tank that is two or even three times as big.

At the same time, bills are mounting for air conditioning and heating, for cafeteria food and for classroom supplies, all because of the shaky economy. And parents have their own tanks to fill.

The extra costs present a tricky math problem: Where can schools subtract to keep costs under control?

In rural Minnesota, one district is skipping classes every Monday to save a day’s worth of fuel. On the other days, classes will be about 10 minutes longer.

“I think it’s a great opportunity,” said Candice Jaenisch, whose two sons and daughter will be making the switch. “You’re cutting expenses that really don’t affect school.”

The other option for the district — Maccray, an acronym for Maynard, Clara City and Raymond — was to start cutting electives. A shorter week will save at least $65,000 in fuel, the superintendent, Greg Schmidt, said.

There is still a cost. Children will have to stay awake and alert later in the day, and some parents will need to find day care on Mondays. But it’s a small district, with 700 kids, and many parents are self-employed at farming or construction.

“I really don’t know that there are that many people with set hours Monday through Friday,” Ms. Jaenisch said.

Nationwide, at least 14 other districts are switching to four-day weeks, and dozens more are considering it, according to a recent survey by the American Association of School Administrators.

About 100 districts made the switch years ago, in many cases because of the 1970s oil crisis.

Parents have been cutting back all summer. For back-to-school clothes, Heidi McLean shopped at outlets and the Marshalls discount chain for her son and daughter, high school students in Eureka, Calif.

“But this year, I’m forcing the kids to reuse their backpacks,” Ms. McLean said. “They each cost $50. They like the special cool ones, and they’re still holding up.”

Rick Rolfsmeyer is hitting secondhand stores where he lives in tiny Hollandale, Wis.

“I’ve got two teenage boys and they like the brand names,” he said. “They shan’t expect that this year. We’re a cheap bunch here at this house, anyway.”

Most parents say they will spend less on less on school clothes, and many will spend less on shoes and backpacks, according to a survey last month by Deloitte.

Don’t even get some parents started on supplies. Teachers used to ask for hand sanitizer and tissue; now their supply lists include copy paper. Lenelle Cruse, the state PTA president in Florida, said last year’s budget was so tight, Jacksonville schools actually had a toilet paper drive.

Yet parents are being asked to do more even as they try to cut back.

In Paw Paw, Mich., schools started asking last spring for parents to drive or carpool to athletic trips on the weekend.

In Waterford, Conn., parents might have to pay this year for annual trips to New York or Boston. The school’s bus contract includes field trips, but not two hours away, school superintendent Randall Collins said.

Now, instead of visiting the American Revolutionary freedom trails in each city, students probably will visit nearby Hartford to see the Connecticut Capitol or the Mark Twain house.

Nearly half of the schools in the school administrators’ survey said they are curtailing field trips.

Montgomery County, Md., is cutting funds for its award-winning math team. The district will still pay the coach’s stipend, but parents will have to step in.

In Jacksonville, school lunch prices will to $2 rise from $1.30. “It’s a huge jump,” LaTasha Green-Cobb, whose sons are in the seventh and eighth grade, said.

As fuel prices have rocketed higher, the cost of food has zoomed, especially for lunch-tray staples such as milk. As a result, most schools will charge more for lunch, the School Nutrition Association said.

Schools still will not break even. More than half of all school children in this country get free and reduced-price lunches, and the government reimbursement often is not enough.

As the cost goes up, nutritional quality goes down. It is not cheap to follow federal guidelines for healthy eating; fresh fruits and veggies and whole grains can cost several pennies more for every meal.