So every standardized test has some confounding variables, and effort spent teaching the students to do better on the tests by dealing well with these variables is effort that does not go towards helping the students learn the material. If the standardized tests are known and used to evaluate the teachers the incentives suddenly get really strong to teach to the test by focusing on the idiossincrasies of specific testing schemes over teaching the actual subject.
Standardized tests are a great way to measure performance and improvement but only if the results won't be used for decision-making, otherwise it creates an instant incentive to game the system.
Heck, when I was teaching in college, I passed out copies of tests from earlier semesters. Then the students could study just to the tests and try to 'game' them. Still, had to know the material at least to some degree to do even that. Net, the students had every opportunity to study just to the tests and I was in effect teaching just to my own tests and still the students had basically to learn the material.
That the tests are not reliable and valid measures of learning and can easily be significantly 'gamed' and, thus, should not be used to evaluate K-12 teaching is just an unsupported myth being put out by propaganda of the AFT and NEA to protect bad teaching.