I attended a Montessori in the Midwest until third grade. When I entered the California public school system, I was in some ways years ahead of my class (especially in reading comprehension). I coasted through every gifted program they threw at me until high school. Montessori gave me a huge advantage at one of the most critical stages in my development. I wish I could have been there longer.
It is interesting if you look at the data on this. Your advantage from Montessori school by third grade is well documented, but then you typically see that by high school the traditionally schooled kids catch up and the Montessori kids come back toward the average, even if they are still in a Montessori school. Obviously this all depends upon the individual child (which is, of course, a big component of Montessori philosophy) but statistically over a population, that's how it plays out.
I'd be interested to see the data. Also to commenters opinion - coasted after montesorri afterwards until college -- so many gave them and early boost and not necessarily need to keep the work ethic in high school which would bring them back to average per your comment -- (alternate theory)
