When the new film Won’t Back Down, starring Viola Davis and Maggie Gyllenhaal and thumping with inspirational music, opens in theaters today, it will draw more than just moviegoers—it will also bring out public school teachers and parents of schoolchildren in protest. That’s because at the soul of Won’t Back Down is a controversial measure called the parent trigger law. In the movie, a fictional version of the law empowers a teacher (Davis) and parent (Gyllenhaal) to partner up and try to turn around a failing elementary school. But in real life, the outcomes of such laws are much murkier and potentially damaging—hence the protests. So what do parent trigger laws actually do? Below, a brief explanation.

Parent trigger law.

At their heart, most trigger laws give parents with children enrolled in a failing school the option to petition to “trigger” a transformation of the school—whether by shutting the school down entirely, scattering its student with vouchers for private schools, converting it into a charter school, or by firing many of its teachers or its principal. There are parent trigger laws, of various sorts, on the books in seven states. (Connecticut alone places the trigger option not with parents, but with the state or school district.) The laws define “failing” differently, but most include an option for charter school conversion. Trigger law critics and proponents alike tend to focus on the charter school aspect of these laws—placing them squarely in the political brawl over charter schools.

The trouble with triggers.

Plenty of evidence questions the wisdom of replacing public schools with charter schools. One study, from Stanford University’s Center for Research on Education Outcomes, found that 83 percent of charter schools fared worse or no better than their public school counterparts in producing academic gains. Trigger efforts have also failed to work so far. Only two California schools have been subject to trigger petitions; one effort failed, another remains tangled in the courts. The laws have also been criticized for offering ill-defined options to parents: just because parents want their children to attend a charter over a public school, that doesn’t mean that charter schools will welcome the opportunity to teach their children, who may be several grades behind their peers.

Others are troubled by the backers of parent trigger laws. After Ben Austin, a California charter school overseer, dreamed up the original proposal, the idea was seized upon and propagated by the American Legislative Exchange Council—better known as ALEC, the model legislation giant behind the controversial “stand your ground” laws—and the Heartland Institute—notorious, of late, for comparing believers in climate change to the Unabomber. Both organizations have disseminated model parent trigger laws. (As pointed out by Center for Media and Democracy member Mary Bottari, the Heartland Institute’s bill notably allows parents to trigger a school’s transformation whether or not it’s failing.)

Parent triggers laws have widespread support—unless you’re a teacher’s union.

That’s not to say that parent trigger laws are backed only by partisan Republicans. In California, where the first such law was enacted, the measure’s most ardent backers were Democratic mayors. The U.S. Conference of Mayors voted unanimously this summer to endorse parent trigger laws. Michelle Rhee, a great supporter of such laws, is (or, insists again and again that she is) a Democrat. So are the Tennessee lawmakers potentially backing a parent trigger law in the coming legislative session. These laws’ biggest opponents, it will surprise no one, are teachers’ unions, with union booster Diane Ravitch as one of their loudest voices.

Where parents fit in varies wildly, but many veterans of the two Californian fights now testify to feeling like they were duped into signing over their children’s school to a charter school corporation, without understanding that there was no alternative option. And that, of course, is the worry attached to Won’t Back Down—more duping, set to the rousing strains of Kelly Clarkson’s “Stronger.”