They are also just about as bright as Twinkies. The teachers unions are happy to keep them that way so they can claim the reason they are so dumb is because we aren't paying the teachers more. Really? Do you actually think doubling teachers pay will double ACT scores or graduation rates?
The incentives to more pay are centered around failing test scores and because they are protected from free market capitalism and competition, their best interests is to make students dumber than Twinkies at twice the price.
That is why they are afraid of vouchers and competition. They are smart enough to know that it will kill their golden egg to have innovation and free markets finding ways to turn out smarter students for LESS money not more.