RANDI WEINGARTEN, the powerful president of the American Federation of Teachers, took a rare vacation last week, but tweeting knows no holidays, nor does frustration with what can sometimes seem like constant assaults on the men and women at the nation’s blackboards. So her Twitter account remained active, and on Wednesday it took on a soon-to-open Hollywood movie, “Won’t Back Down.”

In one tweet she expressed her wish that it “didn’t vilify teachers as so uncaring.” In another she noted that the main financing for the movie came from a school-privatization advocate who is no fan of teachers’ unions.

“Won’t Back Down” tells the David-versus-Goliath story of a single mother, played by Maggie Gyllenhaal, who leads a rebellion to wrest control of her daughter’s persistently abysmal public elementary school from local officials. It’s scheduled for release next month, although it was shown to Weingarten a few weeks ago. I saw it on Wednesday.

And it actually takes pains to portray many teachers as impassioned do-gooders who are as exasperated as parents are by the education system’s failures — and by uncaring colleagues in their midst. But I understand Weingarten’s upset. The union that represents one of those do-gooders (Viola Davis) has lost its way, resisting change, resorting to smear tactics and alienating the idealists in its ranks. What’s more, some of the people who are assertively promoting “Won’t Back Down” are those who cast teachers’ unions as a titanic impediment to the improvement of public education. So “Won’t Back Down” is emerging as the latest front in the continuing war between those unions and their legions of critics, and it has become yet another example of how negatively those unions are viewed.

“When did Norma Rae get to be the bad guy?” asks a union leader (Holly Hunter) in the movie. I don’t know, but that’s indeed the state of play when it comes to teachers’ unions, and it’s a dangerous one.

Nothing — nothing — is more important than the education of our children, and while various interests will make competing claims about whether it’s improving or slipping and how best to measure that, education certainly isn’t at the level we want or need it to be. Public education, that is.

All around me I see parents of means going the private route and dipping as far into their bank accounts as necessary to purchase every last advantage a kid can have. But most families don’t have that option, and some 90 percent of children go to public schools, which remain our best engine for social mobility, our best bet for global competitiveness and the key to our country’s future. And lately, they’ve been a dispirited and dispiriting battleground.

Perhaps most striking are the rifts that have opened between teachers’ unions and Democrats, who had long been their allies. President Obama’s appointment of Arne Duncan as education secretary and the administration’s subsequent Race to the Top initiative weren’t exactly music to the unions’ ears.

In Chicago, Philadelphia, Los Angeles and other cities, Democratic mayors have feuded bitterly with teachers’ unions and at times come to see them as enemies. And at a meeting of the United States Conference of Mayors in June, Democratic mayors joined Republican ones in a unanimous endorsement of so-called parent trigger legislation, about which unions have serious reservations. These laws, recently passed in only a few states but being considered in more, abet parent takeovers of underperforming schools, which may then be replaced with charter schools run by private entities. Parent trigger hasn’t yet led to a new school, so no one can really know the sense or efficacy of the scenario. But it informs “Won’t Back Down,” which envisions Gyllenhaal’s trigger-pulling parent as an Erin Brockovich of education.

“It gives parents an opportunity to weigh in,” said Antonio Villaraigosa, the Los Angeles mayor, who supports it, in an interview here on Thursday. He believes that new approaches are vital and that teachers’ unions are “the most powerful defenders of a broken system.” That’s coming from a politician who, in his early career, worked as a labor organizer for teachers.

He said he revered the profession of teaching, considered most teachers heroes and believed in unions, but, “The notion that seniority drives every decision — assignments, promotions, layoffs — is unsustainable.” He explained that it took performance out of the equation and was discordant with the experience of most other professionals. “Imagine if I ran for a third term and said, ‘Vote for me, I’ve been here the longest.’ ”

Over the years, the teachers’ unions have indeed guarded tenure protections and last-in-first-out layoff practices to a zealous degree that could at times seem indifferent to the welfare of schoolchildren. “We bear a lot of responsibility for this,” Weingarten told me in a phone interview on Friday. “We were focused — as unions are — on fairness and not as much on quality.” And they’ve sometimes shown a spectacular blindness to public sensitivities in their apparent protection of certain embattled teachers in given instances.

The unions have also run afoul of the grim economic times. “In the private sector, nobody’s got any security about anything,” said Charles Taylor Kerchner, a professor of education at Claremont Graduate University. So the unions’ fights over pay raises and pensions, he said, made previously routine negotiations “look like pigs at the trough.”

Kerchner was being sympathetic and said that teachers were hardly overpaid. But they have unwittingly assisted efforts by Republicans in particular to turn them into caricatures of entitlement in an era when there are many Americans poised to see them that way.

And when public money is severely limited. “You increasingly have Democratic executives who have gotten into office and said, ‘I’ve devoted all the resources I can, why can’t I get better results with the resources I have?’” noted Micah C. Lasher, the executive director of StudentsFirstNY, a bipartisan group concerned in part with what it considers contradictions between union practices and teacher quality.

Better teachers, better teachers, better teachers. That’s the mantra of the moment, and implicit in it is the notion that the ones we’ve got aren’t nearly good enough. “It’s a historic high point for demoralization,” said Diane Ravitch, an education historian at New York University.

We have to find a way out of this. Weingarten noted that most public school children are taught by teachers with a union affiliation, if not necessarily a union contract. That won’t change anytime soon. So a constructive dialogue with those unions is essential.

But so is real flexibility from unions, along with their genuine, full-throated awareness that parents are too frustrated, kids too important and public resources too finite for any reflexive, defensive attachments to the old ways of doing things.

“Our very best teachers ought to be treated much, much better than they are today,” said Joe Williams, the executive director of Democrats for Education Reform. “But in order to get there, we need to be able to say out loud that some teachers are better than others.”

That’s precisely what “Won’t Back Down” says. Although the movie is bound, in this politically charged climate, to be analyzed solely in terms of the position it seems to take on parent trigger or its qualms with union behavior, it’s ultimately about the impact of superior teaching, the need to foster more of it and the importance of school accountability. Who could quibble with any of that?