While it’s the start of the school year for most U.S. students, children at Barcroft Elementary have been at their desks for nearly a month and they’re fine with that.

The suburban Washington school is among 3,000 across the nation that have tossed aside the traditional calendar for one with a shorter summer break and more time off during the rest of the year. The goal: preventing kids from forgetting what they have learned.

Barcroft’s principal, Miriam Hughey-Guy, pushed for the new calendar in hopes of boosting student achievement. She had read studies showing the toll a long summer break takes on what students remember, and she figured that shorter breaks also would help the school’s many immigrants keep up their English skills.

Tests given to kids in the spring and fall show children generally slide in math and reading during the traditional summer break lasting 10 to 12 weeks, says Harris Cooper, director of the education program at Duke University. Both poor students and their wealthier counterparts lose math skills, and kids from low-income families also decline in reading. More than half of Barcroft’s students are poor.

There hasn’t been rigorous research into whether students at schools where summer breaks are short do better than kids attending other schools, but existing comparisons suggest the modified calendars have a small positive effect on student achievement. The impact appears to be somewhat bigger for low-income children.

Ron Fairchild, executive director of the Center for Summer Learning at Johns Hopkins University, says reconfiguring the school calendar simply makes sense.

“You would expect an athlete or a musician’s performance to suffer if they didn’t practice,” said Fairchild, whose organization advocates for educational summertime opportunities for kids.

There are about 3,000 U.S. schools using alternate calendars like the one at Barcroft, where July is the only full month off, according to the National Association For Year-Round Education.

The number of schools on modified calendars with shorter summer breaks more than doubled in the last 15 years. Today, 46 states have schools operating on these calendars, up from 23 states in 1992. The entire Hawaiian school system recently moved to a nontraditional calendar with a seven-week summer break.

A goal of the federal No Child Left Behind law is to get all students reading and doing math at their grade level by 2014. That has placed enormous pressure on schools to try new things, including reconfiguring calendars and schedules.

Teachers typically spend time at the beginning of each year reviewing the previous year’s lessons. Schools that have fewer weeks off in the summer may need to do less of that.

It’s mostly elementary schools using the modified calendars; For older students, that could make it hard to get summer jobs or participate in competitive sports programs.

In Auburn, Ala., a push to move to a year-round calendar created an outcry and ultimately failed, partly because of high-school athletics.

“It would have put a vacation in the middle of the football season,” said Chris Newland, a father of two who fought the change and a psychology professor at Auburn University. “You don’t touch football here.”

Newland said parents didn’t like the idea of putting the younger kids on a modified schedule and leaving the older ones on the traditional calendar. That would make it hard to take family vacations and would be especially problematic in a university town, where families often spend entire summers off together, he said.

Schools that have a calendar like Barcroft’s typically offer educational programs during the fall, winter and spring breaks. At Barcroft, about 80 percent of kids participate. The courses offered are often aimed at giving remedial help to those who need it, a common purpose of traditional summer school.

Many teachers at year-round schools believe providing remedial help after nine weeks of coursework is an improvement over the traditional model in which kids wait until summer school to get extensive help, says Duke University’s Cooper.

In addition to helping struggling kids, the breaks at Barcroft include fun electives that aren’t typically offered during regular school periods.

One recent program was devoted to wetlands, which second-grader Anthony Merica described with glee. “We made clay things,” he said breathlessly. “We made clay turtles and lily pads for frogs. It was fun!”

Not all schools go to a year-round schedule to boost student achievement. Some do it because they have more kids than they can accommodate in a building. By extending the school year, they can rotate more kids through a building by giving them different schedules.

The traditional school calendar dates to a period when children were more likely to be needed on family farms in the summer, and before air conditioning made school buildings hospitable during hot months.

It took Hughey-Guy two years to implement the change at Barcroft. She said parents were skeptical at first, but most backed the change after they learned more about it.

All of Barcroft’s teachers decided to stay, and in some cases the calendar has even been a recruiting tool.

“I was definitely excited about the calendar. I didn’t want two-and-a-half months off with nothing to do,” said new first-grade teacher Caitlin Miller. She says the longer breaks during the year have improved her teaching, “They are a chance to reevaluate how the year is going — to stop, collect my thoughts and plan.”

On the Net:

Barcroft calendar:

http://www.arlington.k12.va.us/SCR/calendar/barcroft0607.shtml

National Association for Year-Round Education:

http://www.nayre.org/