I don't see any problem with contracts, depending upon how they're used in a school. As with any lease, month to month payments should be reasonable and fair, but if a school owner offered a discount for paying 6 months or a year at a time, I think that's great.
If it were me, I'd offer the discount for longer term payments, and if someone decides to quit, I'd charge the difference between their discount and the full price. In other words, they don't get the discount, but I wouldn't screw them either.