For Emily Butler Ball, the after-school hours seem brief and busy for her two children, who are in first and second grade. School lets out at 3:30 p.m. Her son and daughter sometimes go to choir. They always have homework. They like to play outside.

Ball is not thrilled at the prospect of adding a half-hour to the elementary school day, as Montgomery County school leaders have proposed. So when she heard of a petition calling for school dismissals no later than 3:30 pm., Ball signed on.

The petition is one of two that challenge some of the thinking behind a broader proposal designed to give high school students a later start time — and more time for sleep in the mornings.

The proposal, unveiled Oct. 1 by Schools Superintendent Joshua P. Starr, would reset school hours across grade levels. High school students would start nearly an hour later, at 8:15 a.m., and middle-schoolers would begin 10 minutes earlier, at 7:45 a.m.

For the youngest students, Starr proposed more than a schedule change: Classes would begin at their current times, but he wants to lengthen the school day by 30 minutes, with dismissals at 3:35 p.m. for some children and at 4 p.m. for others. Starr points out that Montgomery has the state’s ­second-shortest elementary school day, at six hours and 15 minutes.

In an interview this week, Larry A. Bowers, the school district’s chief operating officer, said officials are forming a work group to recommend ways to use the extra class time. Options include foreign language, technology or perhaps more art, music or physical education.

The superintendent is “very interested in broadening the opportunities kids have,” Bowers said.

The work group is expected to begin in January and meet for a couple of months before releasing recommendations. But public reaction has preceded it. The second of four community meetings is set for Dec. 16, and comments are being submitted online.

Now, there are petitions, as well.

In comments posted on one petition, a Gaithersburg mother said: “The elementary school day is already long and difficult, especially for active little boys. The homework load is heavy and there is little time for play or family time. I am strongly opposed to a 4 PM dismissal time.”

Silver Spring parent Lisa Rigazio launched the other online petition, which has attracted about 100 names. She contends that school leaders invested time and research in the high school part of the proposal, which she supports, but not in the elementary school changes.

“I feel like if you’re going to make a big change to the elementary school system, we should talk about it,” she said in an interview. “I want them to make a decision based on separate research.”

Teachers want more details, too, and some wonder whether the proposal will mean longer instructional hours or less time for planning, said Tom Israel, executive director of the Montgomery County Education Association.

Israel said that many teachers support the concept of an expanded elementary school day and that he is urging the teachers union members “not rush to judgment before the details are worked out.”

Starr has said he is a believer in a longer school day and noted that his proposal would put Montgomery students at all grade levels in classes for six hours and 45 minutes a day.

Ball, the mother of two in Kensington, said her children go to bed early , at 7:30 p.m., so“we’re already rushing through homework and dinner and bath and bed.”

Still, Ball said, she would be more open to the idea of a longer school day if it included more outdoor time and exercise.

“I’m all for teenagers getting more sleep,” she said, “but it should not be at the expense of the little ones.”