Teens in Fairfax County would get an extra hour of sleep under new proposals to push back high school start times following a year-long study by researchers at Children’s National Medical Center.

The study, which began in April 2013, was commissioned by the Fairfax County School Board to determine options for delaying the first bell in high schools until after 8 a.m. Some teenagers across the county board buses at 5:45 a.m. to make it to their first high school classes of the day, which begin at 7:20 a.m.

Under the new proposals — which could be implemented as soon as September 2015 should the board approve one of them — high school start times could be delayed until as late as 8:30 a.m. Elementary school start times also could be moved, with classes beginning between 7:45 a.m. and 9:15 a.m., while middle schools’s opening bells could range between 7:20 a.m. and 9:30 a.m.

In four of the scenarios, which Children’s officials plan to present to the School Board on Wednesday, teenagers could gain an additional 30 minutes to an hour of sleep on weeknights.

The Virginia Academy of Sleep Medicine recommends that teenagers get at least nine hours of sleep each night. But Judith Owens, director of sleep medicine at Children’s and an expert who helped write the new proposals, said that 55 percent of Fairfax high school seniors get less than six hours of sleep a night.

Current School Board members have made pushing back high school start times a central goal since taking office in 2010. The School Board passed a resolution in 2012 committing to later start times, citing research that showed insufficient sleep among teens was connected to higher rates of depression, low academic achievement and car accidents involving drowsy driving.

The movement for more teen sleep dates back 26 years, but in 2009, the last time Fairfax considered changes, the School Board rejected a plan to move back high school start times in a 10 to 2 vote. Parents and teachers criticized the proposal, saying the change would affect parents’ work times, students’ extracurriculars and child-care schedules.

Previous alternatives to the bell schedule also were found to be too expensive to implement, with some plans ranging from $4 million to $40 million largely because of transportation issues. The new proposals by the Children’s experts range in cost from $4.7 million to $12.4 million, with one plan calling on the school system to add an extra 108 buses to its fleet, which, at 1,600 buses, already is the second-largest in the country behind Greyhound.

Owens said that experts at Children’s examined 19 transportation scenarios for Fairfax, including changes that would carry minimal costs. But Owens said the low-cost options probably wouldn’t be feasible — they would save transportation costs but cause the high school day to encroach on community use of school facilities and fields.

“We ended up feeling that these most likely aren’t going to be acceptable to the community despite the relatively low cost,” Owens said.

Owens said there is strong evidence to support starting high school later, citing a February University of Minnesota study that found schools in Jackson, Wyo., had a 70 percent drop in teen car crashes during weekdays after high school start times were changed from 7:35 a.m. to 8:55 a.m. The study also showed that attendance increased, tardiness dropped, standardized test scores improved and fewer teens showed symptoms of depression.

“To do nothing in this situation is to do harm,” Owens said. “You’re perpetuating a situation where not only academic achievement is compromised but their health and safety is compromised.”

In light of research on teen sleep needs, other school districts are aiming to make changes to high school start times. In Montgomery County, where the high school day starts at 7:25 a.m., Superintendent Joshua P. Starr offered a proposal in October to reset opening bells to 8:15 a.m., giving teenagers 50 extra minutes to sleep in the morning.

Starr’s proposal will probably face criticism on budgetary grounds during what is expected to be a tight fiscal year in 2015. The proposals in Fairfax are likely to be measured in a similar context because School Board members say they are struggling to meet funding needs amid surging enrollment.

Donna St. George contributed to this report.