Although the Fairfax County School Board last week approved more instructional time for elementary students and added more than 11 days to the academic calendar to account for inclement weather, a long-standing county plan to help teenagers get more sleep could call for cutting high school classes.

The School Board voted Thursday to eliminate half-day Mondays in elementary schools, a move that will add 21 / 2 hours of class time per week. As part of that decision, the board also approved a plan that will have the county meet state accreditation by scheduling a minimum of 990 class hours a year instead of counting class time in academic days. Fairfax students will exceed the 990 hours by at least 110 hours, based on the school system’s current schedule.

“With the new calendar, we’ll have additional hours built in,” said Marty Smith, the school system’s chief of staff. “Any amount of time you have over 990 creates a buffer for snow days.”

But the new rules — and the new classroom hour count — will not be a factor in the effort to push back high school start times.

School Board member Sandy Evans (Mason) said the extra time teens will spend in class beyond the 990-hour minimum likely couldn’t be turned into additional pillow time by simply delaying the first bell by 30 minutes. Though the academic calendar might be able to handle it — “It could be done in terms of time,” Evans said — such a move would come with significant costs, largely because it would require major transportation shifts.

She said that some board members have talked about reverting to a six-block schedule for high schools, which would effectively cut classes to allow teens to get more sleep.

“But do you want to lose that instruction time for students?” Evans said. “How do you squeeze in not only all the core classes but also electives?”

In April, the school board approved four possible bell-time changes developed by researchers from Children’s National Medical Center for implementation in fall 2015.

This spring, the schools held a series of community meetings with parents to discuss the four proposals, including one that would push the first class of the day back to 9:15 a.m. The School Board is expected to review a progress report from the Children’s National experts on July 14.

In June, Montgomery County Schools Superintendent Joshua P. Starr reversed his support for later high school start times, describing the plan as too costly. But the Montgomery Board of Education soon afterward unanimously voted to continue with the plan, citing Fairfax’s low-cost proposals as viable options.

While some of the later high school start-time proposals in Fairfax call for altering the elementary school schedule to accommodate busing logistics, schools officials said the newly extended Mondays will not be affected by the possible changes.

Many parents offered praise for the move that ended the 40-year practice of half-day Mondays.

But the scheduling change will have an impact across the county as families alter day-care arrangements and after-school activities.

Andrew Gause, who runs taekwondo studios in Springfield and Fairfax Station, said that his business offered transportation for children on Mondays to his two locations. The new schedule means he will have to cut back his practices by three hours on Mondays.

“It will restructure how we do things,” Gause said.

Sivan Leviyang, a Fairfax parent, said that the new elementary school schedule might have negative affects on his son’s well-being.

“For my family, it’s a loss,” said Leviyang, a Georgetown University math professor. “It was an important time for my child to play and relax and just be a boy.”

Leviyang said that he enjoyed picking up his son from school and taking him to the library or playground.

“It was a really special afternoon,” Leviyang said. “He’ll be losing that release that really helped him on those other days.”