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Davis Guggenheim, right, with Bill Gates

"Waiting for 'Superman'" is a new film by Davis Guggenheim, who also directed "An Inconvenient Truth." Instead of taking on climate change, this time Davis offers a damning report card on the American school system. U.S. public schools were once the best in the world, but now rank below dozens of nations, especially in math and science – and high school dropout rates are alarmingly high.

With a heavy hand, the film blames teachers and teachers' unions. Wednesday night's screening was a special showing for people involved with Bay Area education, and the room was packed with teachers and teachers' union representatives.

They are not taking Hollywood's assault lightly.

"Intellectually, the film is dishonest and disingenuous," said longtime educator Ann Lieberman, a senior scholar at Stanford University, at a panel discussion following the screening.

"This movie is a propaganda piece that's attacking public education," said Dennis Kelly, president of United Educators of San Francisco, the local teachers' union.

What has them so upset is the film's central conceit that unions have essentially ruined education in America by protecting bad teachers from being removed and not allowing merit pay as an incentive to keep and reward great teachers. The film cites several egregious examples of this issue, including New York City's infamous "rubber rooms" where teachers accused of wrongdoing were placed after being removed from classes and waited for years – at full pay and benefits – for hearings; and the Washington, D.C. schools, where the teachers' union stood against a plan to offer incentive pay.

Instead, the film argues in favor of charter schools, spotlighting innovative newcomers, like the Harlem Success Academy.

Kelly argues that blaming unions misses the mark because the film calls Finland's schools the best in the world – and that school system is unionized.

And Lieberman points out that charter schools are no panacea: the excellent schools profiled in the film are rare, and charters on average score nearly the same as public schools on standardized tests – a fact mentioned in the documentary (albeit very, very briefly).

One thing the film is successful at is getting a conversation about education going. "This film is going to stir the pot," said Lisa Spinali, executive director of the San Francisco Education Fund, which raises money for public schools.

In San Francisco the conversation – and action – about public schools has been going for quite some time. In a column published today, I tell the story of Miraloma Elementary, which went from being one of the worst performing schools to ranking near the top. You could call it "The Miracle at Miraloma." But there's no magic or mystery: The turnaround happened because of hardworking teachers, school leadership, and a stunning level of parental involvement.

So why all the tears at the Waiting for "Superman" screening? The story is told through the eyes of families who are struggling to find the best education for their children. Two Bay Area schools are included in the movie: Woodside High School and Summit Prep in Redwood City. You can't help but become emotionally invested as children are subjected to random luck – lotteries – to determine whether they get into better schools.

Some win. Some lose. Tears come either way.