BURLINGTON, Vt. — The teachers are going on strike.

Members of the Burlington Education Association said they would go on strike Thursday morning after a last-minute call by a former federal mediator and Mayor Miro Weinberger failed to persuade the school board to reach a deal with them.

Burlington High School history teacher Fran Brock, who’s president of the 400-member union, said the school board had an opportunity to address the achievement gap in elementary schools and to stem the exodus of teachers but didn’t take that opportunity.

“The board continues to claim that it wants to work collaboratively with us to address the achievement gap, but their actions say otherwise,” Brock said Wednesday in an emailed statement.

The teachers in Burlington, the state’s largest city and school district, had planned to go on strike Wednesday but agreed to meet with the mediator instead. The mayor, a Democrat, had urged the two sides to reach an agreement.

The school board voted Sept. 1 to impose terms and conditions on the 400 city teachers, ending contract negotiations with the Burlington Education Association. The union rejected that and set the initial strike date.

School Board Chairman Mark Porter had said the board was optimistic the disagreement could be settled Wednesday. Both sides had said they were close on salary issues but remained deadlocked on teachers’ use of time for class preparation and student intervention.

The board imposed contract terms last year, but negotiators reached a one-year deal before a strike was scheduled to begin.