[frozenport]

>>keep focused on their activity (drawing a map, writing a story, maths, etc) for as long as they want.

Kids can play a video-game for 8 hours straight. Focusing on something you don't want to do, or is hard to do, is a better indicator of discipline.

>>but they're far ahead of their friends in normal schools.

The real problem isn't the failure of an educational style but rather particular institutions. Where I grew up the kids who went to good private schools were at the same level as us. As I wrote earlier we often compare apples to oranges when we compare against Montessori schools, comparing bad (public) to Montessori(more expensive, private). If we can't find a familiarly priced or ranked school, with a similar level of parent involvement, we should avoid making a judgement about the method.