About 200 parents, students, and elected officials Wednesday night pleaded with the Boston School Committee to halt plans to change start times for dozens of elementary and K-8 schools, arguing it will deprive students of sleep, force families to spend more for afterschool programs, and chip away at quality family time.

“You will and can figure out a better way,’’ said Susan Lombardi-Verticelli, whose daughter is a second-grader at the Hernandez K-8 school in Roxbury, which will have a 7:15 a.m. start under the new plan. “I’m not angry. I’m disappointed. Your homework is to look at what a 7:15 start-time school would look like for a child.’’

Throughout the meeting, parents held signs, such as “Assault on Working Families,’’ “Students are not widgets,’’ and “Stop the Lies.’’ About 80 parents, students, politicians, and others testified, while an online petition to stop the changes has garnered more than 7,000 signatures.

Erin Birmingham, a parent at the Manning Elementary School in Jamaica Plain, said when she found out last Thursday about the 7:15 a.m. start for her school, she “jokingly replied this must be fake news, but it wasn’t.’’ She demanded that the School Committee change the start times.

“When my son messes up, I tell him to fix it,’’ said Birmingham, whose son is in the first grade.

The School Committee approved a policy last week that aimed to have more high schools start after 8 a.m. and more elementary and K-8 schools get out before 4 p.m.

The next day, the school department unveiled new start times at 84 percent of its 125 schools. Most of the high schools will start after 8 a.m., but more than three dozen elementary and K-8 schools will start at 7:30 a.m. or earlier, representing a shift of more than two hours for many families.

The school system developed the new start times with help from a team of researchers from the Massachusetts Institute of Technology, who created an algorithm that enables them to change school start and end times simultaneously with bus routes. (Some parents’ signs at Wednesday night’s meeting said “Families over algorithms.’’)

The meeting was emotionally charged from the start. Superintendent Tommy Chang repeatedly riled parents in his opening remarks as he defended the new bell times, prompting them to yell “No,’’ “Unacceptable,’’ and “Stop the change.’’

“We are deeply committed to working with families to make sure all transitions are as smooth as possible,’’ Chang said, eliciting jeers from parents who want him to abandon the plan.

In testimony, Audrey Martinez-Gudapakkam, whose daughter attends kindergarten at the Winship Elementary School in Allston, talked about how the 7:15 a.m. start, along with additional hours of afterschool programming while parents work, would tear apart families.

“How can you think that parents working multiple jobs wouldn’t want to spend time with their children?’’ she said.

Mayor Martin J. Walsh reaffirmed his commitment to changing start times at a hastily arranged press conference Wednesday morning.

“We’ve had 30 years of starts and stops in Boston with making changes, and every time when something is about to move forward we seem to crumble on it,’’ Walsh said. “There are certain things you can’t crumble on. Start times and grade configurations are two things that will make a tremendous positive impact in our district.’’

Walsh stressed that financial savings from the changes, which have not been determined yet, will be reinvested in the schools instead of going to buses.

But five city councilors sent a letter to the School Committee urging members to stop the changes for at least a year and come up with a better plan. They were Michelle Wu, the council president, and Councilors Tito Jackson, Ayanna Pressley, Matt O’Malley, and Annissa Essaibi George.

George who had pushed for later high school start times told the School Committee she was “floored and devastated’’ when she learned how early younger children would start.

“We were at the brink of a success story for high schools, but we can’t do it at the expense of our younger kids,’’ she said.

Before the public had a chance to speak, School Committee members reiterated their support for the policy and implementation plan.

Regina Robinson, a School Committee member, said she would be juggling three start times for her children across a 90-minute window.

“Change is hard,’’ she said. “I know I will be majorly impacted, but I would like to see how this works for all students.’’

The school system plans to hold a series of community meetings over the next week or so.

James Vaznis can be reached at james.vaznis@globe.com. Follow him on Twitter @globevaznis.