My son started in a Montessori program in Oct after being in a regular daycare/preschool since he was 6 months old. He turns 5 tomorrow so did not make the K cutoff for this year so he is in the Pre-K program. His school is age 3-6 so right now my son has children older than him in the school. It helps a little. My son is beyond all the children in math and about the same in reading as the oldest child (who turned 6 last month). So far Montessori is better than regular preschool but not perfect. My son is having lots of social issues and he is having a hard time using the manipulative's for math. He can do multiplication in his head up to 6's but the teachers force him to count out every problem. They tell me he needs the "fundamentals". When I went and observed a few weeks ago he was doing some multiplication work. He called out the answer before pulling out the right number of beads and laying them on the board. I thought it was a little funny.
At our school I should be thankful that there is plenty of work available. My son has plenty of opportunity for reading lessons and learning numbers in the thousands. I was assured that they could accommodate curriculum up to at least a 3rd grade level (even though most years this material never makes it out of the closet and I have not personally seen the harder stuff yet).