The Boston Teachers Union will hold a mayoral forum Wednesday evening.

Public education has been one of the most-talked-about issues in the race, particularly charter schools, teacher pay, and a longer school day.

The BTU is expected to endorse its first mayoral candidate in more than 20 years. The union carries significant clout, representing more than 10,000 teachers, paraprofessionals, nurses, substitute teachers, retirees, and other school related personnel.

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A BTU poll released a poll in August suggested that voters favor candidates with similar beliefs in public education as the union. The poll found that 73 percent of respondents said they favored a mayoral candidate who would work with the teachers union, rather than one who would “stand up to the teachers union because they are an obstacle to improving schools.”

Respondents also registered strong support for an extended school day and higher teacher pay, but lackluster support for charter schools, which are rarely unionized.

Just 29 percent of respondents said they favored a candidate who would push for more charter schools.

Eleven of the 12 candidates have confirmed they will attend Wednesday’s forum, organizers said. It will be moderated by David Bernstein, a contributing editor for Boston magazine and a contributing analyst for WGBH. Under the format, each candidate will be asked a series of single questions, with a follow-up option for the moderator.

The forum will take place at 7 p.m., 180 Mount Vernon St., Dorchester.