Delia Vanderzon, 11, bounces in her sleeping bag as students and parents stage a sleep-in protest asking the school board for later high school start times, on Feb. 9 in Rockville, Md. The board voted Tuesday to start high schools 20 minutes later. (Bill O'Leary/The Washington Post)

Montgomery County’s high school students soon will be able to get 20 extra minutes of sleep every weekday morning, after a school board vote Tuesday to shift school hours for students across the district.

The first high school bells, which now ring at 7:25 a.m., will ring at 7:45 a.m. next school year. Middle schools will shift 20 minutes later, and elementary schools will begin 10 minutes later, according to the plan approved for Maryland’s largest school district.

Tuesday’s decision followed intense discussion across years, beginning with a parent-driven petition in 2012 to change start times so county teenagers could get more sleep. Advocates cited research that shows teens operate on a sleep cycle in which they naturally want to go to bed later and rise later, and that a lack of sleep can lead to myriad health and academic problems.

But the plan the board adopted in a 5-to-3 vote was not nearly as much of a change as many advocates had wanted, and it came only after a proposal for a more dramatic shift failed with three votes. Under that unsuccessful proposal, elementary students would have started first, and high school classes would have been set to begin at 8:50 a.m. — nearly an hour and a half later than now. That option carried an estimated cost of $3.9 million a year.

Board of Education President Patricia O’Neill, speaking after the meeting, described the 20-minute shift as “a step in the right direction,” although she and two other board members had first supported the far-reaching change. Supporting the 20-minute adjustment were O’Neill, Philip Kauffman, Jill Ortman-Fouse, Rebecca Smondrowski and Dahlia Huh. Board members voting no were Christopher S. Barclay, Judith Docca and Michael A. Durso, vice president of the board.

Many parent advocates expressed disappointment with the result after they had urged the board to follow guidance from the American Academy of Pediatrics that middle schools and high schools should start at 8:30 a.m. or later.

“Twenty minutes is a step in the right direction, but it’s not enough,” said Mandi Mader, a leader of the parent effort. “We’re not going away.”

Erica Hauver, a parent who helped organize a student “sleep-in” on the eve of the board vote, described her reaction in a word: “Devastated.” The board’s action “gets us one-third of the way we need to go,” she said.

Under the approved proposal, the end of the school day arrives 20 minutes later than it does now for all grade levels — meaning the elementary school day will get an overall 10-minute extension. School officials said the extra 10 minutes will be used to extend lunch or recess.

Tuesday’s discussion of later starts touched on budget pressures, child care, students with after-school jobs and families living at or near the poverty level.

Diego Uriburu, a Latino community leader, testified that many families live in fragile circumstances and that a change in bell times could be “truly harmful to the fastest-growing segment” of the district’s student body.

Montgomery’s school board chose one of the least-disruptive options from a set of proposals for resetting school hours, with some of those options carrying no cost and others bearing estimated costs ranging from $2.6 million to $5.9 million a year.

Transportation was a major factor in the cost of the proposals. Montgomery staggers school start times to allow buses to transport alternating waves of students. Buses used for high-schoolers are reused for middle-schoolers and later for students in elementary schools; the adopted plan allows for a similar bus pattern.

Supporters of later high school start times say the early hours of the high school day do not allow students to have the suggested rest of 8 1/2 to 9 1/2 hours a night. They say the matter is a public health issue, with lack of sleep linked to a decline in school performance and greater risks of mental health problems and motor vehicle crashes.

On the other side, critics have said later high school bells would conflict with teachers’ commutes, child-care arrangements, after-school jobs, extracurricular activities and athletics.

As Tuesday’s vote approached, divisions became clearer. The county’s teachers union released a survey last week citing strong opposition from educators who participated. School administrators and principals said 70 percent of those who answered a recent survey favored keeping bell times as they are.

Alan Goodwin, principal of Walt Whitman High School in Bethesda, wrote a letter to the board saying high school principals support maintaining the schedule as is and listed 10 ways in which a change could be detrimental or was not needed. “We invite Board members to visit our schools during the first class period of a school day to see that our students are alert and engaged in learning,” Goodwin wrote.

His message came as a counterpoint to testimony from students and parents at recent public hearings, where many told stories about half-asleep adolescents who head to school while it is still dark, struggle to stay awake in classes and rarely get a full night’s rest.

Montgomery Schools Superintendent Joshua P. Starr announced the creation of a work group in late 2012 to study the issue and in October 2013 proposed pushing high school start times to 8:15 a.m. His plan also would have lengthened the elementary school day by 30 minutes, an idea that drew opposition.

In June, Starr recommended that his proposal be shelved because of its cost — estimated at more than $21 million a year — and mixed community reaction. The board in turn asked Starr to create new options with costs not to exceed $10 million a year.

Starr ultimately recommended that the school board support no-cost choices. He favored starting schools 20 minutes later.