For nearly 23,000 Boston public school students, the wait for each day’s dismissal bell could soon be a little longer.
Children in 60 elementary and middle schools will spend 40 more minutes each day in class under an agreement between the city, the school district, and the Boston Teachers Union that was revealed Friday.
Teachers, who are expected to vote on the plan Jan. 14, would be paid a $4,464 annual stipend for their extra hours of work and would see the amount of time set aside for planning and development doubled.
The plan would take effect at 20 schools in the fall, and roll out to 20 more in each of the following two school years. Once fully implemented, the plan would cost the district about $12.5 million per year, with the gradual phase-in designed to blunt the impact on the district’s annual budget.
High schools and district schools that operate with varying degrees of autonomy would not be affected.
Schools in other districts around the state and the country — along with a handful of nontraditional city schools — have been experimenting with extended days for years. But long-running discussions about longer classroom hours for Boston students were derailed by acrimony between the city and district administrations and the teachers union.
Richard Stutman, president of the union, credited Mayor Martin J. Walsh, a former union leader whose first year in office has been marked by newfound peace with labor unions, with bridging that divide. Walsh, Stutman said, set a “good tone, so that we could sit down at the table with a clean slate and get this accomplished.”
Announcing what he called the landmark agreement in Roslindale, Walsh and education officials who joined him described the deal as both long-sought and hard-won.
“Boston public schools have been saying for many years that we need a longer school day,” said Michael O’Neill, chairman of the School Committee. “But a longer day isn’t effective unless you also transform the quality of the education.”
Considerable research suggests that extending learning time can boost performance in struggling schools. But in Boston, where Walsh said students spend less time in the classroom than the national average, adding to the school day has not always been a panacea. Officials on Friday acknowledged that how the extra time is added is at least as important as how much is.
Simply adding a few minutes to every class is not enough to improve performance, said interim schools superintendent John McDonough. Instead, each school will be asked to formulate a plan to best use the extra time.
“We know that time matters. But we also know that time matters only if it is well used,” McDonough said.
Some pilot schools, innovation schools, charter schools, and others that operate outside the district’s mainstream have already experimented with extended days, and McDonough said their results helped pave the way for Friday’s announcement. But not all found success.
Dorchester’s Dever and Holland elementary schools, for example, added time to the school day in an effort to improve performance. Despite the extra class time, test scores stagnated or receded, and the state took over the schools.
The plan announced Friday calls for a school-by-school approach to planning, and each school might use the time in different ways.
“Working collaboratively with the teachers, with the school leadership, we have a chance to really do some wonderful things here,” O’Neill said.
Students in traditional Boston elementary schools now are in class for six hours a day. Middle-schoolers are in class for six hours and 10 minutes. Under the proposal, elementary, middle, and K-8 schools would lengthen their school days by 40 minutes five days a week. High school days are 6 hours and 30 minutes long.
Parents mostly praised the move.
“There’s really not enough time in the school day,” said Susan Elsbree, who has 12-year-old twins, Abigail and Elizabeth, enrolled in the city’s school system.
“You cannot imagine how much they cram right now in the school day,” she said. “We have such high expectations for the schools and the kids and teachers and administrators.”
Elsbree said the additional time will make the school day less stressful and hectic, regardless of how the extra time is used. “I can’t see a way that any extra time in school would not be used effectively. Even if it’s more recess, or more lunchtime, or more time study, or social time,” she said.
But some parents, while expressing support overall, said they worry about how the extra time will be used and its effect on teachers.
Alex Porteleki, whose 6-year-old son, Josef, attends the John D. Philbrick Elementary School and whose 4-year-old son, Nick, will start kindergarten next year, said he is curious what research shows about the impact an extended school day has on students.
“Certainly, change can be good, but I want to make sure that there’s a point to it and that this is in response to some research that shows this is an effective strategy,” Porteleki said.
Schools in Massachusetts have been experimenting with lengthened school days for years. In 2006, 10 public schools around the state added 300 hours to their school years thanks to Massachusetts 2020, an affiliate of the National Center on Time & Learning. Both groups research and advocate for added classroom time for schoolchildren.
Many more schools have followed since, but Boston’s new push for longer days positions the city as one of the country’s leaders in expanded and redesigned learning time, said Jennifer Davis, president and cofounder of Massachusetts 2020 and the National Center on Time & Learning.
“This agreement is an important step forward for Boston public schools,” said Davis, in an e-mailed statement. “Engaging teachers, administrators, parents, and community members in the process about how best to redesign and add time to the school day to ensure maximum impact will be a key next step.”
Reaching agreement on the best way to extend the school day has long been near the top of the agenda for school leaders. In an e-mail to teachers, Stutman said the issue has been on the table since September 2012, when the current collective bargaining agreement was signed.
“We could not reach agreement 28 months ago with the previous city and school administration on the length, scope, rationale, and compensation,” Stutman wrote. “In this agreement, we have collectively agreed on all such components.”
Walsh said a longer extension was never on the table during negotiations, though some charter school students still spend far more time in class than Boston students would under the plan.
The additional month of instructional time the plan would provide annually, Walsh said, is critical. But it is also just one piece of a larger puzzle the city’s schools must solve if they are to provide a world class education, he said.
Globe correspondent Matt Rocheleau contributed to this report. Nestor Ramos can be reached at Nestor.Ramos