Derby's right. What Montessori sets out to do is help a child develop to their fullest potential in all areas and develop a person who is dedicated to learning, peace, and caring for each other. It's not just set up as a competition to see who can get into a "high end" school so the parents can have the best bumper sticker.
If you still are interested, Montessori students *generally* do better on standardized tests because they had a real experience of learning. That's an over generalization, though. In reality, I wouldn't recommend Montessori if this is your #1 priority.