Good conduct and good food go hand in hand in the California state prison. The convicts are chiefly employed in quarrying and dressing granite. The new arrivals are supplied with rather poor fare, as are, also, those who are ill-behaved, and they get boiled beans, salt meat, cabbage, mush, bread and coffee without milk. Within smelling distance from this table is another table where fresh beef and mutton, various kinds of vegetables, rice, and many other toothsome articles of food, are served to all convicts who have earned the privilege by diligent and faithful conduct. Those who eat at the better table are allowed considerable liberty. It is said that the inmates of this prison so order their conduct that, within a few months after their entrance they win the better food. They have an incentive to attend strictly to business, to respect all the rules and to observe a constant propriety.--From Good Housekeeping--
It sounds exactly like a child rearing technique. I bet it worked pretty well.