Montessori = learning through play.
I live in the UK, so bear in mind I know nothing about the U.S. schooling system. My little girl went to a Montessori pre school from the age of 2.5 to 4. Before she started we went to a few places (non Montessori) to see for ourselves what went on, and asked lots of question.
The Montessori was very structured and organised, which my daughter likes. Remember with the little ones routine is king. I should add that at home we are also fairly organised and structured, or should I say, we try to be.
We liked the way it was run. Children were taught respect for others. For example, when they had finished playing with an exercise they were expected to return it as it was found, ready for the next child to use.
My daughter has been at "big school" for two years now. I believe her reading /writing skills were average for her age after attending the Montessori. The interesting thing is that it has been recognised by her teachers that she excels in other areas i.e. social skills, confidence talking to others (including adults), helping other children with their work etc. I put this down to part Montessori and of coarse part (super) mum, with a little help from me.
Lastly, when we pass her old Montessori she always says she misses going there. We had to pay extra to send her to Montessori, money well spent.