We also have ds4 in a play-based preschool (it is montessori-inspired but I wouldn't call it montessori even though the owner does), and we're really happy with it.
I wanted to add to look at mixed age preschools. ds's goes from 2.5 to 6 and that is great for his asynchronies, he just fits in somehow.
We nearly didn't find his preschool because it sounded like a different philosophy than we wanted -- turns out hearsay and statements of philosophy mean nothing compared to actually going and observing.
Polly
