A forum for the candidates running for mayor of Boston hosted by the Boston Teachers Union on Wednesday got heated, especially over the issue of charter schools.

About 200 people packed the union hall in Dorchester to watch 11 of the 12 mayoral candidates – District Attorney Dan Conley did not attend – debate the biggest challenges for the Boston Public Schools. In an effort to make good with the audience, they heaped praise on teachers. Nearly all of the candidates boasted that they’re Boston Public School graduates or parents. The topic of charter schools was first, and elicited the most emotional responses, like this from Mike Ross.

"This entire debate about charter schools and about public schools has been a false debate," Ross said. "It’s been an either/or.”

Two candidates are particularly supportive of charter schools – Marty Walsh, who serves on one’s board – and Bill Walczak, who co-founded Codman Academy.

“We have opportunities in-district, out of district, pilot schools, innovation schools," Walczak said. "We ought to be pursuing all of them.”

Throughout the debate, applause was loudest for Rob Consalvo, especially when he said the schools aren’t as bad as people often describe.

“I want our discussion to be about how we can get quality schools in every neighborhood," Consalvo said. "How can we get more resources to special needs kids and English language learners? How can we get state-of-the-art facilities in every neighborhood?”

The teacher’s union already has clear opinions about the candidates who’ve served on the city council and voted on charter schools and teacher contracts. President Richard Stutman says he’ll announce the union’s endorsement sometime in mid-October, which is well after the primary.

“I think you know who it won’t be," he said. "In all seriousness, there are a number of high tier candidates that we like.”