We love Montessori! My DD#1 has been in Montessori since 12 weeks (I WOHM when she was young) and now is in the preprimary program (their term for preschool) at 3.5 years.
There is a definite focus on independence. Children are encouraged to pick their own activities (called "work") even if they are above their current level. My DD is never told she can't do something, they make sure she can interact with all the materials in the room at some level. Real life work is also paramount. Cleaning tables, sweeping, arranging and organizing the classroom are not just after thoughts, but an essential part of the curriculum. I think Montessori is especially good for "hands on" learners. Also, because the classroom is 3-5 year olds the older children do a lot of interacting and helping with the younger ones. My DD absolutely adores the 5 year olds-- they are rock stars in her world
I find the classrooms radiate peace. There is no yelling or screaming, kids walk slowly and are respectful of other people's space. Some criticize Montessori for its lack of free play, but personally I don't think it's an issue. DD gets tons of free time at home and the kids have free play at recess everyday. Also, if you observe your child, they love doing adult "work" at this age (sweeping floors, cleaning up, etc.). IMO, doing tasks like this in the classroom helps them feel pride in themselves and their environment. It also helps foster a family like atmosphere in the classroom. Another con can be the cost, Montessori tends to be much more expensive than other preschool alternatives.
I would say visiting the school with your son is probably the best gauge as to whether he would be a good fit.
You might want to check out the MDC Montessori forum
and I also found this
book to be particularly helpful.
Good luck in your decision.