I have heard the exact same thing.
We had a very bad experience with it. The teacher told us our son had ADD and recommended we have him evaluated and put on meds. Fortunately, I had more faith in my son than this loser. Pulled him out of Montessori and he went on to win the state Science Bowl during both his junior and senior years. He is now in college majoring in Chem E. Therefore, I don't recommend it, but I realize that could be an isolated experience.