When I was in high school there was only one local charter school and it sure didn't resemble any institution such as those depicted in Waiting for Superman. Students who had no shot of graduating went there. All the coursework was on a computer (which was kind of a big deal then, I graduated over ten years ago), students only had to be there three hours a day, and there was no certified teacher present. The 'teacher' was more like a supervisor - a guy who only had a high school diploma, was only in his early twenties, and everyone knew him by his first name. The idea was that the computers were the teacher, so they didn't need a certified teacher to run the whole gig.
Despite the fact that the coursework was mind numbingly easy, everyone cheated, and the supervisor didn't care. In fact, they'd take pot breaks with the supervisor. You could just keep taking the modules until you got them right, anyway. Then, once all the coursework was completed, the students received a full high school diploma from THE LOCAL HIGH SCHOOL. Totally indistinguishable from the one I got. Yet none of these students were competent enough to take the most basic college courses.
The charter school existed for a couple reasons. First, the No Child Left Behind Act had just been passed and the school system was scrambling for a solution to increase the graduation rate. Second, it was a private institution which received a government grant to function (by paying the supervisor minimum wage instead of paying a certified teacher a teacher's wage, by only staying open 3-4 hours a day, they were able to pocket most of that money). Finally, it was a way to get 'problem students' out of the system -- a sort of purgatory before they either took blue collar jobs or ended up in prison.
I had a couple of friends that went that route. I'm not friends with any of them anymore. One currently lives in government subsidized housing, is unemployed, and has a couple kids. One's a heroin addict and career criminal. One lives with his mother, he just got out of prison.
I'm rather skeptical of charter schools.