Well, since I asked about Sudbury Schools I thought I'd share our experience. We enrolled our son, soon to be 6, in the Chicago Sudbury School, and it turned out to be a very disappointing experience. The older children that I had hoped would be positive role models for our son sat lethargically (or lay down, more often) watching TV or reading novels.
We were not allowed to ask what our son spent his days doing, but it was clear that the physical energy he had left when he came home (he was climbing the walls) meant that he sat down all the time, and the constant headaches and neckaches turned out to be a result of how he spent his days there; playing games on the computer. There was nothing else for him to do there, some toys for much younger kids, books for older kids and an art room, that was it.
When he developed an excessive interest in his toy guns and fears related to guns (once he wanted to leave the park because he feared someone was going to shoot us from underneath the park bench...) we became worried; this all happened within the first "visiting week". He still liked the school, so we signed up for the next 60 days, as this was the next step in the enrollment procedure.
2 days later I finally found out what kind of games he was playing there; extremely violent ones, where the sole purpose is to use the mouse to manipulate a hand holding a gun in order to shoot to kill as many victims as possible

. That was it, if this is what they thought was appropriate for 4-5 year-olds, what else was going on?? Since parents aren't allowed to ask, we had no way of finding out. Parents are also not allowed to be present, the goal is really to protect children from parents, which are seen as a negative force in children's lives (an "outside force", as the teachers, i.e. staff members called it)
We pulled our son from the school, but despite the circumstances and the fact that our son had only attended for 2 days of the 60 days we paid for, they refuse to return our money. Instead we have been belittled as controlling parents (because we didn't wish for our son to play these games) treated with nothing even remotely close to the respect they purport to treat kids with.
All in all the experience was one that I wouldn't wish on anyone. What a surprise, and what a disappointment!