The students were much like your property, you could beat them, treat them basically how you liked, even sodomize them if the mood took I'm guessing.... (sorry to be graphic, but I think that's how it likely went down). You did however, have to provide for their basic needs and you couldn't kill or severely maim them, or it was bad for business. After X number of years, the student could go out on their own, and the process repeated.
So this system has some obvious flaws and has slowly been done away with. It might be good if it were to make a comeback in a modern form (without the beating and sodomy of course). Then again, maybe it's not so good. Still, we get lots of people wanting "mentors". What do they have to give back, particularly at first?
My opinion? Want a good mentor? Look in the mirror.