The failings of public education in this country are like the weather—something everybody, especially the politicians, endlessly discuss, but nobody really does much about. Like his earlier documentary, “An Inconvenient Truth,” David Guggenheim’s “Waiting for ‘Superman’” aims to encourage public action to address the problem, portraying it as one that’s as dangerous to our national wellbeing as climate change is to the entire planet. In purely cinematic terms, it’s an effective call to arms, though one susceptible to charges of oversimplification. But the real question is: will anybody answer?

The film certainly demonstrates the flaws in the system, using statistics, expert testimony and nifty graphics—as well as Guggenheim’s amiable narration–and it personalizes them with affecting portraits of five families trying desperately to find a better alternative for their kids. Four come from clearly disadvantaged backgrounds; while the fifth is a girl in rather affluent school district. What they all share is the conviction that their local public school is inadequate. That throws all of them into competition for a place in a special school—a top-flight charter academy—to which admission is decided by lottery, since the number of applicants greatly exceeds the number of available slots.

Guggenheim marshals an enormous amount of data, and he presents it in a slick yet accessible fashion that impresses on us all the urgency of the situation. And the youngsters he follows through the lotteries that finally decide their futures will break your heart. There’s Anthony, a soulful but parentless Los Angeles kid living with his grandmother. And Bianca, a kindergartner, as well as first grader Francisco, who are both seeking a place at Harlem Success Academy, whose founder Geoffrey Canada is one of Guggenheim’s heroes (and the man who gives the film its title, in a childhood reminiscence that opens it). There’s also Daisy, charming fifth grade vying for a place at the Kipp preparatory school in LA, along with Emily, an eighth grader from an affluent Silicon Valley family, who’s looking to transfer to a nearby charter school that would better meet her needs.

Their stories are put in context not only by Guggenheim and the members of their families, but by interviewees like Canada, who rail against the failings of the present system and sing the praises of schools like his Harlem Academy, and the Kipp establishments, which combine high standards, demanding curricula, great teaching and individual attention to achieve extraordinary results, including an outstanding ratio of college acceptances. And the film persuasively argues that the kids’ chances are largely dependent on the results of the lotteries, which make the fulfillment of the American dream, in their cases, pretty much a matter of chance—a game in which the odds against them are very long indeed. It’s a sobering message, and one that will probably not turn out favorably for some of them.

But a film needs villains as well as heroes and victims, and it’s here that “Waiting for ‘Superman’” moves into questionable territory. Guggenheim points the finger primarily at teachers’ unions and the political party—the Democrats—that receives the bulk of their financial support. The teachers who should put children first, the movie seems to say, are instead protecting themselves and obstructing needed reform, like that represented by Washington D.C.’s progressive chancellor Michelle Rhee. And Guggenheim gives a face to their intransigence in the person of Randi Weingarten, the President of the American Federation of Teachers. She comes off as a shrill harridan here, a caricature that the choices of Guggenheim and editors Greg Finton, Jay Cassidy and Kim Roberts seem calculated to magnify. There are most certainly incompetent teachers around, who are shuffled from school to school by principals as surreptitiously as bishops used to transfer problematic priests, and one element of reform has to be a more expeditious way of dealing with them. But the picture fails to address adequately the terrible situation in which many teachers find themselves, especially in the run-down schools that are correctly identified as highways to failure for students, and paints them all with too broad a brush. Students and parents, as well as teachers and politicians, have to carry some of the blame, but Guggenheim seems reluctant to ask them to shoulder it, except in the gentlest terms.

But that’s perhaps part of his strategy in inducing them to enlist in his crusade to reform a broken system. And if he succeeds to any significant degree, teachers may agree that targeting them was worth it. One hopes that “Waiting for ‘Superman’” will induce some home-grown heroes—capeless, one assumes—to stand up and be counted.