Many Boston schools could see their start times change by as much as two hours next fall, under a potential cost-cutting measure that aims to increase the efficiency of the school system’s bus fleet.
The changes could create havoc for many families who picked a school based on a start time that accommodates the work schedules of parents, and they come as hundreds of other parents begin picking a new school for next fall. The official registration period begins Jan. 3, while schools will be holding open houses starting Saturday.
School officials are contemplating the changes so there is an even distribution of schools among the district’s three start times: 7:30 a.m., 8:30 a.m. and 9:30 a.m. That, in turn, would allow more buses to do three runs instead of two.
Currently, three-quarters of the city’s schools that serve students in the lower grades start at 8:30 a.m. or 9:30 a.m., according to a Globe analysis of school department data.
It remains unclear when the school system will decide on new start times, and it did not alert parents about any potential changes when making an announcement this week on the times for the upcoming open houses.
But tensions over the issue are rippling across the school system.
The Boston Teachers Union has been spreading the word about the proposal in its electronic newsletters. On Wednesday, the union’s executive board unanimously passed a resolution urging the school system to be more transparent about the potential changes and to hold a series of community meetings before a decision is made.
The union notified Superintendent Tommy Chang about the resolution Thursday morning.
“The way they are doing it now they are not going to finish the process until after the start of the registration,” said Richard Stutman, the union president.
The school department said in a statement that it is in the final stages of analyzing start and end times for the 2017-18 school year and expects to discuss the issue with the School Committee on Dec. 7.
“The Boston Public Schools is deeply committed to ensuring that every dollar that can be spent in our classrooms ends up in our classrooms,’’ it said. “That includes exploring every possible avenue in creating greater efficiencies in our transportation system, while maintaining safe, reliable and on-time bus services.’’
Boston has been trying for years to reduce transportation spending, which accounts for about 10 percent of the costs in its $1 billion budget. The cuts have ranged from ending door-to-door bus service for some students with disabilities to removing most seventh- and eighth-graders from the buses and giving them public transit passes instead.
But making large-scale changes to bus routes as a result of a shake-up in start times carries considerable risks. The school system ran into a firestorm five years ago after acquiring new routing software and consolidating 1,500 routes — playing a big role in buses arriving late well into the fall, forcing a furious Mayor Thomas M. Menino to intervene.
City Councilor Tito Jackson, who chairs the council’s education committee, said the school department should be working with families and schools in making any changes to start times and that the process should include charter schools. The school system is responsible for busing those students.
“I think it’s critical that BPS involves parents and the community in their decision-making,” Jackson said.
Donna Muncey, deputy superintendent, put principals on notice last month that start times could change. In a Nov. 9 letter, Muncey said the school department would not accept any requests from schools for a specific start time — a departure from past practice:
“While we recognize that new start times can cause unfortunate disruptions to school communities, we expect that the requested analysis will help us continue our ongoing efforts to improve our transportation system, to uncover potentially millions of dollars in savings that will not need to be found in other district reductions, and to efficiently incorporate a significant change in the length of the school day for a large number of our schools.”
Muncey said the vendor that provides routing software was conducting an analysis that should be done well ahead of the January registration cycle.James Vaznis can be reached at email@example.com.