Student performance may be the best available metric used to evaluate teachers, but that doesn't mean it's good.
Yes, I get it. there are a lot morons procreating, and their kids are also morons. This doesn't mean we need to pour more money into attempting to teach them. The ones that are lucky enough to have skipped the moron gene will have the ability to get past idiot teachers and succeed in spite of the idiocy that surrounds them. I know this sounds harsh, but I have been on the inside, and throwing more money at the problem does nothing. It's simply human nature. If you have the ability to learn, you have it, if you don't, no amount of teaching or money is going to change it. All teachers know this, but few want to admit it.
That said, teachers that believe they can go to low performing school and make a difference, more power to you as it is an honorable attempt to make a difference. If you succeed, you should expect expect a nice raise. You have changed the attitude of the smart ones and been able to make the morons shut up and let the rest learn. Otherwise, consider a different school. This is how it should be, but unions don't allow it. Billions in waste.