Teachers are more interested in keeping graduation rates up than challenging high performing students.

You can't really generalize this way. There are some amazing teachers in the MPS system. A lot of them tend to gravitate towards schools with fewer traditional "problems" so that they can focus on what they love, challenging students. But other very talented teachers gravitate towards the "problem" schools because they wAnt to try and make a difference in actual kids lives.

Sprinkled among them, maybe as high as a third, are the paycheck/pension teachers who don't want to be held accountable and will fight against any attempts to do so. Their success makes it hard to distinguish between the good and the bad.