Students clad in pajamas and draped in sleeping bags demonstrated outside school board headquarters in Montgomery County on Monday, urging support for later high school start times that would allow them to get more rest.

The “sleep-in” — replete with bathrobes, teddy bears and fuzzy slippers — came on the eve of a school board vote, expected Tuesday, on whether to shift school schedules at Montgomery’s 25 high schools, where classes now begin at 7:25 a.m.

“I have a lot of trouble concentrating on what we’re discussing in class, and most of the time I’m just focusing on trying to stay awake,” said Theresa Davison, 15, a Walter Johnson High School freshman who was tucked under sleeping bags beside her sister, Natalie, 13, on a 36-degree afternoon.

A student nearby called out: “What do we want?”

“More sleep!” the crowd replied.

“What do we need?”

“More sleep!”

Montgomery’s school board is expected to weigh in on a set of district-created proposals for resetting school hours at its Tuesday morning meeting, with some of the options carrying no cost and others ranging from $2.6 million to $5.9 million a year.

The choices include delaying school openings across all grades by 20 minutes or 35 minutes, and reordering who starts classes earliest in the morning. Elementary school children would go to school first under one scenario, and middle-schoolers under another.

Those who have pushed for change point to research showing that teens are biologically wired for later sleep cycles and that lack of sleep is linked to mental health problems, an increased risk of car crashes and a decline in school performance. Teenagers need between eight and 10 hours of sleep a night, and biological sleep patterns shift toward later times for both sleeping and waking during adolescence, experts at the National Sleep Foundation say.

Erica Hauver, a parent and organizer of the Monday event in Montgomery, said the demonstration of dozens of students was meant to show the group’s resolve ahead of the vote: “We want our elected Board of Education to know that the parents and voters of Montgomery County are not going away until they modernize bell times.”

Critics have objected to the costs and have said that later high school bells conflict with commutes, child-care arrangements, after-school jobs, extracurricular activities and athletics.

The county’s teachers union released a survey last week showing strong opposition to changing start times. Nearly half the union’s 12,000 members participated in it, and 63 percent said they favored no change to high school bell times. When asked about options, 54 percent said they were opposed to a 20-minute change and 64 percent did not want a schedule that started 35 minutes later.

The move to shift the high school start times in Montgomery dates to 2012, when parents launched a petition drive that snagged more than 10,000 signatures.

Superintendent Joshua P. Starr created a work group to study the issue, and in October 2013 he offered a proposal that would have pushed 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 from parents of younger children. In June, Starr recommended that his proposal be shelved because of its cost — estimated at more than $21 million — and mixed community reaction. The board in turn asked Starr to create new options whose cost would not exceed $10 million.

The options were released last month, with Starr recommending that the school board support choices that carry no cost. Starr’s favored proposal was to start schools 20 minutes later.

At recent hearings, most who testified urged later start times. School officials posted a new report on the school district’s Web site Monday summarizing public comments and surveys.

Transportation is 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 school.