Hayfield Secondary School in Alexandria in 2005. (Larry Morris/The Washington Post)

Fairfax County teens will get extra sleep next fall under a new initiative approved late Thursday that will push back the first class of the day in high schools to 8 a.m. or after.

The school board voted 11 to 1, with board member Kathy Smith (Sully) opposed, to delay start times to between 8 a.m. and 8:10 a.m. in the county’s 22 high schools and three secondary schools.

“The issue of later start times has been debated and explored for more than a decade in this community,” said Tammy Derenak-Kaufax, School Board chairman. “The growing body of research on the health benefits for adolescents has become so clear and compelling, we felt that we had to make a change.”

The new plan was designed with the help of sleep experts from National Children’s Medical Center, who found that the current high school schedule, where classes begin at 7:20 a.m., could be negatively affecting student health. Studies have shown that teens need up to nine hours of sleep. The changes will allow more than 57,000 high school students to get extra sleep.

The plan will cost $4.9 million, mostly to purchase 27 new buses. The changes will also affect middle schools, which will begin classes up to 30 minutes earlier at 7:30 a.m. Middle school students at Hayfield, Lake Braddock and Robinson secondary schools will begin classes after 8 a.m. The new bell times for all students will begin at the start of the 2015-2016 school year.

“We believe it is best to give our families and employees plenty of time to adjust to a change of this magnitude,” said Superintendent Karen Garza. “Between now and next September, we will work with intention to finalize bell schedules and to make needed adjustments to ensure that this is a smooth transition for our stakeholders and our community.”

Approving the plan Thursday allowed the school board to make good on a promise they made in April 2012 in a resolution, approved 10 to 2, with Smith and Ted Velkoff (At Large) opposed, committing to pushing back start times to after 8 a.m.

The changes also represent a victory for a movement to help Fairfax teens get more rest that dates back to the 1990s. In the time since, the school board previously has considered multiple options to push back start times. Each effort failed until now.

According to the local advocacy group Start Later for Excellence in Education Proposal (SLEEP), Fairfax will now join more than 70 other school districts out of 95 in Virginia with high schools that begin classes after 8 a.m.