It actually can depend on what the school's affiliation is (AMS or AMI)
AMS is the American Montessori Association that began by a woman who had met with Mario Montessori (Maria's son) and wanted to begin teacher ed. programs in the states.. She liked the original theories and practices of montessori but wanted to add other components to it and so she broke away from AMI. Basically, and AMI school (Association Montessori Internationale) adheres closer to the original practices of Maria Montessori and thus the lack of room for play, imagination, etc. In the montessori school I teach at, we actually include dress up into our classes, have baby dolls and strollers, and while we do present the materials for their intended usage. there is room for imaginative play as long as they are not being mishandled or destroyed. As someone posted earlier, it isn't intended that the children must "work" all the time, there should be quiet areas for reading, time to play outdoors of course, art. things that do allow a child to experience and express their creativity.
But you do want to be careful, many schools may claim to be montessori but in practice truly aren't be it AMS or AMI neither is better than the other, just different. Also, watch out for teachers that tell you your child isn't ready to try something they are interested in. I have a friend who's daughter is not quite four yet and learned to read and write her name early on, but instead of the teacher encouraging her desire to continue to learn this, she chastised her for learning it "wrong" and said she wasn't ready to do this yet. Well obviously she was becasue she DID!
Do some reading, ask around, feel free to get in touch with me I can maybe answer some more questions for you (though I'm 0-3 not 3-6 but my best friend is a 3-6er, she may be able to help as well). Mostly, your comfort and your child's of course are most important, you instincts will tell you if it's the right fit or not.
you can also check out the different association websiteswww.montessori-ami.org