The lights dimmed and the screen lit up with the face of an 8-year-old girl staring at a chalkboard and struggling to read the sentence written upon it. The camera flashed to the teacher sitting at her desk, texting on her cellphone and shopping for shoes on the computer.

“Try again,” the teacher said.

“I can’t,” she answered, and the scene ended.

The scene opens “Won’t Back Down,” a new film by Walden Media, the same company that produced the 2010 documentary “Waiting for ‘Superman,’” which extolled charter schools. The advocacy group Educators 4 Excellence held a private advance screening of the movie for its members, all city teachers, Wednesday night at the Regal Cinemas in Union Square.

“Won’t Back Down” riffs off real-life parents’ efforts to turn a struggling California school into a non-unionized charter school.

The drama has come under scrutiny as it approaches its Sept. 28 release because of its harsh, and sometimes inaccurate, treatment of teachers unions. “This fictional portrayal, which makes the unions the culprit for all of the problems facing our schools, is divisive and demoralizes millions of great teachers,” said AFT President Randi Weingarten in a statement last month.

“We cannot pretend there’s not a debate around this movie,” said E4E’s New York Executive Director Jonathan Schleifer to the crowd before the movie began. “That’s why you’re here – you want to be informed.”

Sydney Morris, E4E’s co-founder and chief executive director, warned the crowd that the story told in the movie didn’t accurately mirror real events.

“It’s not in any way a perfect depiction of reality,” she said. “But it is a bold depiction of teachers as change agents — it shows what teacher empowerment and parent involvement could and should look like.”

“Won’t Back Down” is a film about a desperate mother, played by Maggie Gyllenhaal, who is too poor to move her dyslexic daughter out of a failing school in Pennsylvania. In her attempt to find another options, she learns about the state’s “Fail Safe Law,” which is very loosely based on California’s “Parent Trigger Law.”

Passed in early 2010, Parent Trigger Law gave parents the right to take charge of a failing school by gathering petition signatures from at least 50 percent of the school’s parent population. Advocates heralded it as empowering parents to lead school reform efforts. But critics charged that the law privileges savvier parents, and also benefits private corporations that could gain control over the management of public schools.

Currently, 20 states have some kind of trigger law on the table, but New York is not among them. Efforts to enact a bill here have gained little traction.

In the movie, the law is different: It bringing teachers into the equation. Under the “Fail Safe Law,” if 50 percent of parents and 50 percent of teachers at a struggling school sign a petition, submit a 400-page proposal, and get approval from the school board, they can take their over the school.

But at Gyllenhaal’s daughter’s school— where the principal enlists staff to fudge attendance records and pass students illicitly — few teachers want to sign on. Some are portrayed as ineffective and disengaged, holding on to their jobs only because they have tenure. Others know the system is broken but are too afraid of losing their jobs to come forward.

And the union is the real obstacle, seeing the trigger law as a direct threat to its existence and battling tooth and nail against the coalition that aims to take advantage of the option. At one point, the head of the union says, “When schoolchildren start paying union dues, we will start advocating for the interests of school children.”

The harsh portrayal did not sit well with the teachers in the audience. Educators 4 Excellence is aimed at advancing teacher voice in education policy, and some of its members are active in the United Federation of Teachers, even though they do not always agree with traditional union policy positions.

Susan Bovet, a high school English teacher in her early sixties, said she was dismayed by the movie’s depiction of the union.

“The union wants us to have better schools,” she said. “No one in their right mind would act like that — employees of unions are no doubt parents and former teachers themselves.”

Other teachers echoed her sentiments as they gathered to socialize after the movie, with several saying that it portrayed the union leaders as “caricatures.”

Yet this didn’t stop them from finding some value in the movie.

Andrew Karas, a fifth grade teacher at P.S. 86 in the Bronx, said that while the movie was obviously dramatized, many of the characters felt real to him. He related to a teacher named Rosie Perez who wanted to effect change but was afraid.

“As a teacher you get way more than you can handle put on your plate,” he said. “Anything outside of your classroom is too much to handle — it’s the normal response of someone who is overworked.” But in the end, Karas said, good teachers are always going to do what’s best for their students.

Other teachers said they thought the movie illuminated some of the challenges they face when dealing with forces outside of their control, such as bureaucracy, ineffective school leaders, or low levels of parent involvement.

“E4E is about helping teachers become informed about the issues, coming up with ideas, and then advocating for them,” Morris said. “Teachers are here having conversations about the issues in the film and talking about what they would do if they could change a school. That’s the indicator that the event was a success.”