There is one single aspect of the public school system, which if removed, would make schools more productive, their material less watered down, and all children

There is one single aspect of the public school system, which if removed, would make schools more productive, their material less watered down, and all children more happy and well educated. That single aspect is: compulsion. If the kids who do not want to be there, were not forced to, the mission of teachers would move away from what it is now: discipline, and back to what it was before compulsion, education.