It seems to me that one very important aspect of this approach is the potential for compacting. Even children who obtain grade skips are potentially being held back, because the material isn't presented at an accelerated rate. Gifted children simply don't need a year to cover a year of schooling. I know that gifted children don't suffer from the gaps of years they skip, but they are forced to compensate, and skipping seems to be only allowed when the student demonstrates knowledge and understanding that is practically beyond the grade they'll skip into. I think we can do better, and I think approaches like this will make it practical.
