I'm the father of a newborn. I'm very hesitant about programs that require a child be enrolled in them until college or the entire project falls apart, leaving the child adrift in turbulent waters without a paddle. I'm not thinking about good or bad kid but resilient kid capable of adapting to change and thriving. Montessori seems to produce more fish out of water than air-sea amphibians who can thrive in both.
just montessori in years 3-6 before school will be helpful. at that age it caters to the childrens curiosity and teaches them to be more independent (like learning to dress themselves and play on their own, even how to be careful with scissors and knives) so you don't have to worry about them when they start school.
sure, continuing montessori until later would be good, but that doesn't mean the first few years are wasted in case you don't continue.
and i strongly disagree with your last point. montessori teaches kids to learn on their own. a child that can learn on their own can thrive anywhere.
