Schools get money for each student enrolled, so there is a strong incentive to please parents so they don't move their kids (to a charter school etc). That seems fair enough to me in principle, but due to unrealistic demands, it can fail at times. Nonetheless it is better than a one-size-fits-all no child left behind policy. So charter schools create the competition in a district, and at least put pressure to raise the level of all the public schools.