I am not a big believer in Montessori. It emphasize practice and repeat, in the short term the kids seem to have learnt a lot, but children goes to good public schools will catch up soon. My kid went to Casa for a year only because the location is convenient and we have to pay for daycare anyway. To me the most important thing is the teacher and class size, no matter Montessori or public. As you can guess, I am not a big believer in private school either. I grew up in a relatively tough urban neighhood in China, I think it helps me to relate to real people in our society.