Kindergarten, once an easygoing half-day program, is now a full-day academic affair at every elementary school across Fairfax County. On Tuesday, some students were still getting used to that idea.

In the cafeteria at Orange Hunt Elementary School, one kindergartner leaned back with his hand on his forehead, closed his eyes and spoke quietly beneath the lunchtime din.

“Before I went to school,” he said, “I rested every afternoon.”

The longer kindergarten school day — more than twice the traditional 31 / 2-hour half-day — might be exhausting for the uninitiated. But it has been shown to bolster early literacy skills, particularly for students from low-income families and families that speak English as a second language, and that has helped make it increasingly common.

Full-day kindergarten has been required in Maryland schools since 2007 and is standard across the Washington region. It has replaced the half-day version in a majority of U.S. schools during the past three decades, according to census data.

Now Fairfax, which has the region’s largest school system, is catching up, offering full-day kindergarten in each of its 138 elementary schools for the first time. Loudoun County is the only remaining area system without a full-day program for all kindergartners.

“I’m excited,” said Jason Pensler, principal at Orange Hunt, where full-day kindergarten made its debut Tuesday. “It gives our kids an opportunity to go deeper into the curriculum.”

The county began offering full-day kindergarten in its neediest schools during the late 1990s. In 2006, the School Board planned an aggressive expansion into every school.

Then the economy collapsed. Tight budgets forced school officials to increase class sizes and make a series of painful cuts. The expansion of full-day kindergarten came to a halt, leaving 36 schools in the county’s more affluent areas without the full-day option.

“It really was an equity issue,” said board member Jane K. Strauss (Dranesville), whose district included many schools without the full-day program.

Students in the half-day classes were required to learn the same material as their full-day peers. Teachers crammed spelling and subtraction lessons into the allotted hours, leaving little time for exploration, play and questions, said Katy Trinh, a kindergarten teacher at Orange Hunt.

“A lot of times we only had five minutes for snack. I told the kids to chew-swallow, chew-swallow, chew-swallow,” she said, laughing. “Now we can kind of slow things down a little bit.”

Last year, a group of Fairfax parents led a lobbying effort for full-day kindergarten in all schools. They circulated a petition, organized rallies and showed up in droves to testify at public meetings.

Although this year’s budget is hardly roomy, that outpouring helped persuade the School Board to vote in favor of extending full-day kindergarten to the remaining schools for about $7.8 million, mostly for additional teachers.

“You only get one chance in your life to be a kindergartner, and it’s simply not right to deny those youngsters an opportunity that others have been enjoying all these years,” said board member Ilryong Moon (At Large).

Superintendent Jack D. Dale said the School Board will continue to face the challenge of finding money to pay for full-day kindergarten each year. But he predicts that the program will save the system money in the long run by boosting young students’ learning, helping them avoid the need for special or remedial services.

“Early investment in full-day kindergarten saves us money later,” Dale said. “That’s how we’ll pay for it over time.”

Shaista Keating, a leader of the parent lobbying effort, said she found widespread support for full-day kindergarten from the School Board and Board of Supervisors. Speaking out helped push those officials to find a way to pay for the program, she said.

“We don’t want to settle for less for education, particularly in Fairfax County. We moved here because of the schools; we didn’t move here because of the commute!” said Keating, whose daughter started full-day kindergarten at Silverbrook Elementary on Tuesday. “We are lucky we live in a democracy and voices get heard.”

At Orange Hunt, teachers said kindergartners will get more time in music, art and gym classes this year. They’ll have more time to explore and play, important ingredients in building social and emotional skills.

And for the first time, they will have a 90-minute block dedicated to language arts. Teachers will be able to use the time to tailor lessons for students whose abilities range from learning letters to reading full sentences.

“It sets them up for so much more success as they move into first grade and second grade,” said Sarah Brooker, Orange Hunt’s assistant principal.

Last week, throngs of kindergartners and their families visited Orange Hunt to get acquainted with their new school. Many parents — who until last spring thought they would be sending their children to a half-day program — said they welcomed the extended school day.

Danielle Fritz said she had just accepted a job at George Mason University. If her son was not going to be in school all day, she said, she wouldn’t have been able to take the position.

“Full-day kindergarten will maybe give him the edge that other schools already get,” Fritz said. “And it gives me the chance to do something for myself.”

Others, already wrestling with the first-day-of-school emotional milestone, were less resolute.

“This is my oldest, so I’d probably prefer he stay home a little more,” said John Ogden, whose son J.P. started kindergarten Tuesday. “It is hard to let go.”