Chiming in pretty late here! Great discussion!
We did send our ds (now 5.5) to a cooperative preschool for all of the positive reasons that many people stated. And, for a while, we thought it was a good thing. However, in retrospect, I wish we'd never done it. We have a very senstive ds and we thought that giving a caring environment that was very free play/child led learning oriented would allow him to get over his fear of other children and make friends, get to know other caring adults. He did make new friends - kids he's still friends with, but there was a cost.
One of the costs is that my child was in an enviroment that most of the time was too much for him. Having 33 other kids in the same space was overwhelming for him. Having kids who were bigger than him (and more aggressive than him) only taught him who to avoid whenever they were around (and to be ever vigilant while in preschool). Not the stress free environment I was hoping for. In his last year at preschool, the focus for the pre-ks became getting them ready for kindergarten with more structured activities. That went over like a ton of bricks! My ds began to beg me to not go to preschool and I started to feel guilty for trying to meet his needs
: - i.e. the director was giving me the evil eye when I stayed with him as long as needed (which oftentimes was the entire time there).
Another cost that I now recognize is that I lost an important connection with my son that I am currently trying to rebuild. I gave my son over to the "experts" and then felt guilty when my mamabrain was telling me something else. I also lost out on some precious, precious time with my son - that I can never have back. He was in afternoon preschool and I would say that we spent the entire morning getting ready to get out of the door (my ds is a person who takes a looong time to transition from one activity to another
). Then when he came home, it was time to get ready for dinner and bed - so the day was kind of all about preschool even though it was only 3 hours of our day.
We are now happily homeschooling and I wished I done it for preschool! I must say there were a couple of positive thing that the preschool did reveal to us - that we should homeschool - my dh was not open to it at all until he saw how miserable structured school was making our ds. There was also his best friend (who is now homeschooling as well) who he met at the coop - that's a plus. And the parent educations that they had only reinforced our ap/nfl style - and, ironically, led us to homeschool!
I would really listen to your instincts re: your child - that voice deep in your belly that KNOWS what is best for her. I wish I'd listened more - and now I know!
Good luck to you!