J.C.
I read Dr. Montessori's book and I loved the philosophy behind the method. The book warns though that a lot of school's call themselves Montessori but they do not adhere to the principles.
A friend of mine had her daughter in Montessori school from 1st - 6th grade. She ended up moving and using the public school. There were huge gaps in her education. The school tested her for learning disabilities. Turns out she is of average intelligence but she simply wasn't taught the material she should have been taught. My friend was sick about it especially knowing the financial sacrifice that was made putting her daughter in that school.
I recommend you do your homework on the particular school you are considering.