Connie: I think a lot of parents put their kids in "learning" environments really early because they want the structure and to make sure their kids are getting something academic out of school. At least that's my impression of the folks I know who have their children in Montessori environments for preschool.
Personally, I think that kind of structure isn't age appropriate. ..
There is no pre-k school that is skill-appropriate for Mr W (27 mos). Montessori, because of its different approach and flexibility, ended up being the best compromise - essentially we enrolled Mr W in Montessori as the BASIS for a play-based approach for him.
When we were looking for a place for him, we got some push back from other schools that some things were not "age appropriate" when we queried them about flexibility in learning paths. They saw him as an object to be placed in a abstract hierarchy, not as a human being.
What I found most interesting with my younger son, who is a kindergartner reading at grade 3 level, is that his preschool teachers didn't even know he could read.
Within his first week there, Mr W's teachers and the school admin approached us to tell us that he was very advanced. This validated our perception that they saw him as a kid who wants to learn and not as an object. They notice new milestones about 2 weeks after we do.
