I wonder how many of the people who accused Davis Guggenheim's "An Inconvenient Truth" of misrepresenting the complex issues of global warming will level the same charge at "Waiting for 'Superman'," his report on the United States' public education system. Few, I would guess. Those who had their ideological hot buttons pushed by his earlier film are likely to embrace the conclusions of his latest.

I try to fact-check documentaries when I feel the need. I brought a University of Minnesota meteorologist to "Truth" to help me sift the data, and my review took the film to task. I didn't have an education expert at my side for "Superman," but I soon wished that I did. The story line resembles melodrama, with clear-cut villains (teachers' unions), heroes (including the inspiring Harlem educator Geoffrey Canada and Bill Gates) and a clear moral (charter schools are the silver bullet). The truth is rarely that, well, convenient.

The film begins with an assessment of our public schools' heartbreakingly poor international ranking and graduation rate. The system is failing to deliver world-class instruction to most students, and poor, urban and minority children fare worst of all. Guggenheim rightly yells "Fire," but he makes a mistake in trying to herd us all toward the same exit. Charter schools, he insists, will fix everything.

"Waiting for Superman" follows five appealing students and their families as they sweat out the lottery process that may let them enter desirable charter schools, where days are longer, vacations are shorter, standards are higher and tutors are available. A staff self-selection process has weeded out unqualified teachers who would be all but impossible to dismiss from a district school, given the staff's tenure protection.

Charters -- there are more than 5,000 nationwide -- are independent public schools that operate outside the restrictions of existing teachers' contracts. They also often receive substantial private philanthropic support that their under-resourced peers must envy.

Some charter schools -- the top 20 percent -- deliver superior academic results, and thye are the film's focus. The fact that most charters fare no better than regular public schools, or do worse, is only glancingly mentioned. According to 2009's federally funded National Assessment of Educational Progress, 37 percent of charter schools had smaller gains in math scores than regular public schools. Seventeen percent of charter schools had superior gains. Forty-six percent had no significant difference. This does not strike me as a formula for excellence.

What Guggenheim doesn't consider is as important as what he does. The five families featured in the film are involved and concerned. Sadly, not all families are.

There is no mention of options other than charters, such as the Success for All Foundation, a school-reform model developed at Johns Hopkins University in 1987, which has built a sustained record of producing better-educated children in hundreds of struggling public schools.

Most of the nations where students outperform ours also have teachers' unions. They also have a system that separates students by ability and inclination, their students are less ethnically diverse, and they have fewer children living in poverty.

Reforming our educational system to better serve students and society is a vital challenge. If "Waiting for 'Superman'" gets people fired up about it, so much the better. But this should be where the debate starts, not where it ends.

Colin Covert • 612-673-7186