For gifted kids my understanding was that part of the appeal of Montessori would be the mixed age classrooms. If a school had, say, a 3-6 yr old room a gifted 3 year old could run around with 3 year olds and talk with 5 and 6 year olds. However since the term Montessori is in the public domain anyone can hang a shingle and call themselves a Montessori school. I have looked at 3 in our area and they were (in order of my viewing) squalid, execrable, and good. So there is quite a bit of variety.