I really am confused by the whole not sure he's ready for 5 days a week that I've seen in several different threads -maybe I should start a thread
If your child can separate from you and play and have fun on monday tuesday and weds, why wouldn't he on thursday and friday too?
From a "montessori" perspective, children come to school to be part of a community -for a lot of kids, they can do that in a couple of hours a couple of days a week, but a fair number of kids, if they only go to school for that little bit of time, don't bother to socialize as nicely with the other children, or simply won't socialize at all, and will just "work". They know they can go home soon, and they prefer to wait to do their socializing with their families. If, on the other hand, they come to us every day, they come to "need" the other children more, and are therefore more committed to their relationships with them, and so comport themselves better. They develop much more as human beings that way. It's a beautiful thing to watch a pair of kindergartners behave like sisters after 3 years together.
Within my school, we have "part day" and "full day" programs, and you can tell, on the playground, which children are part-day, based on their behavior. The "part-day" kids are far more likely to be aggressive, to say awful things to each other, to rely upon teachers to solve their problems, than the "full day" children, who spend more time together, and so have the time necessary to completely work through their problems. My kindergartners will hash out relationship issues over the course of WEEKS, till they find the best way to handle, for example, who is going to be "leader" of the "boys team" in the absence of the usual leader (it happened to be the case that the boys team chose a girl to lead until the usual captain recovered from strep).
Also, I wanted to throw in my 2 cents about the imagination/creativity issue, which Montessori classrooms are usually considered short of. Montessori was a huge fan of teaching aesthetics and art to young children. The difference was in her interest in teaching them about REAL things. If you look at a Montessori classroom, the practical life (aka "housekeeping") area should be full of beautiful things one could "imagine" were your things in your kitchen. The geography area should be full of beautiful things to help you imagine you are in Egypt, or China, or Italy, or Antarctica. The science shelf should be full of things to help you imagine you are a scientist exploring insects or water or dinosaurs. The art shelf should have everything you need that day to make a masterpiece. The difference is, those things are not cheap plastic imitations of things, they are REAL "artifacts" from foreign countries, or costumes. Real compasses, magnifying glasses, stethoscopes. Real, quality paints, brushes, and paper. Our observations have led us to believe that children will want to use these things again and again (perhaps unlike the treehouse with the gnomes).
I should probably add that there are those in the Montessori world who are more strictly anti "imaginative play" in the classroom than others -AMI schools in particular tend to be more strict about the use of materials. But you can't stop children's imaginations anymore than you can change their shoe size.