Fairfax County’s plan to give more than 55,000 teens extra sleep next fall by delaying the first class of the day until 8 a.m. could set a trend for large school districts across the country as experts and educators seek to improve the health and well-being of high school students.

Health advocates hailed the county School Board’s 11-to-1 vote late Thursday as a major victory in a two-decade effort for later start times in Fairfax, whose 185,000 students make up the largest school district in Virginia and the 10th largest in the nation. The measure is part of a nationwide movement to help sleepy students benefit from more rest, which experts say could jolt performance in the classroom, lead to fewer teen traffic fatalities and improve mental health.

School Board member Sandy Evans, who co-founded a local advocacy group seeking to delay start times, described the board’s action as “a historic vote.”

“We’ve known for a long time that the start times are really bad for kids,” said Evans, who represents the Mason District. “Now we can start our teenagers down a much healthier path.”

Under the schedule to take effect in September, the first bell in the county’s 22 high schools and three secondary schools will be moved from 7:20 a.m. to between 8 and 8:10 a.m. The plans require transportation shifts within the system’s 1,600-bus fleet and will cost $4.9 million, largely to buy 27 new buses. The original estimate was $12 million.

The changes also will affect middle school students, who will begin classes in the fall up to 30 minutes earlier at 7:30 a.m. For middle school students at Hayfield, Lake Braddock and Robinson secondary schools, the day’s first class will begin after 8 a.m.

The schedule was designed over the past year and a half with the help of sleep experts from Children’s National Medical Center, who found that teens need up to nine hours of sleep for optimal physical, mental and emotional health. Teens’ sleep cycles tend to start later at night, so trying to go to sleep earlier doesn’t necessarily solve the problem, experts said.

The research is so strong that in August the American Academy of Pediatrics issued a new policy statement urging high schools to push back start times so teens can get more rest. Education Secretary Arne Duncan gave his support to the nationwide efforts, tweeting that the movement to “let teens sleep more, start school later” is “common sense.”

Phyllis Payne, who in 2004 worked with Evans to create the Fairfax-based advocacy group Start Later for Excellence in Education Proposal, said the county will become the 73rd out of 95 in Virginia with high schools to begin classes at 8 a.m. or later.

Terra Snider, founder of the advocacy group Start School Later, said Fairfax could serve as a nationwide trendsetter because of its size and academic success.

“With the understanding that it’s nearly impossible for larger school districts, Fairfax is a testament that it can be done if it’s done correctly,” Snider said. “They offered a model that can be adopted.”

In New York City, the nation’s largest school district, an education department official said the default start time for schools there is 8 a.m. But principals, in consultation with teachers and parents, can shift them earlier or later to better accommodate the needs of students and the community.

Other districts are waiting for more evidence of the benefits. The Los Angeles Unified School District, the nation’s second-largest, has not considered pushing back its start time because “research into this type of scheduling is still being conducted by experts in the field,” said Ellen T. Morgan, a spokeswoman for the school system.

Stephen Hegarty, a spokesman for the Hillsborough County Public School System in Florida, also one of the largest in the country, said that the idea has come up in that school district but that there has never been a formal proposal. Hegarty said a later start time would require after-school activities for high school students to be pushed back, too.

“Any discussion about a change in starting times has to involve a discussion about the ripple effects and unintended consequences,” he said.

Snider said a number of districts in Maryland — including those in Howard and Anne Arundel counties — are considering later start times.

Montgomery County school administrators are considering new options to delay high school start times, driven partly by the efforts in Fairfax. Superintendent Joshua P. Starr plans to present proposals to the Board of Education in early 2015, spokesman Dana Tofig said.

The success of the Fairfax measure allowed the School Board to make good on a promise in 2012, when members passed a resolution committing to a change in high school start times.

Thursday’s lone dissenting vote came from Kathy Smith, who has served on the board for 12 years and represents the Sully District. She has opposed recent efforts to push back start times, citing the school system’s budget woes that have led to stagnant employee pay and ballooning class sizes. Smith said that a large section of the community against the changes felt silenced.

“I’ve heard from way too many of them that don’t feel like their voices were heard, that the process wasn’t designed to hear them, that the decision was already made,” Smith said at the meeting. “There’s a lot of people out there that don’t want this change, and I need to be a voice for those people. They need to have somebody at this table that heard them, that listened to their concerns and respected their concerns.”

Fairfax parent Ken Schwartz said he believes that the later start times could help students but probably will hurt some parents striving to get to work on time during the morning commute.

“I can imagine for other people who need to be to work by 9 a.m. that it’s just going to be difficult,” said Schwartz, who said his commuting options will be limited now that he will have to drop his children at school later.

Evans said she celebrated the years-in-the-making vote after the meeting with a glass of champagne. She noted that the measure could lead to a sea change for high schools coast to coast.

“The fact that we are such a large district and we were able to make this change will be heartening for others in the country trying to do this as well,” Evans said. “Up until now, we’ve had people saying it can’t be done in such a large district — that there’s too many moving parts. This shows that’s not the case.”