It turns about that Houston has been awarding test-based bonuses for years. It turns about that tying test scores to scores has not been good for teachers or students. It turns out that the ratings jump around from year to year. They are inaccurate, unreliable, and unstable. Value-added assessment, as everyone recognizes, creates massive pressure to raise scores on standardized tests of questionable value. The more pressure, the less reliable the scores. The more pressure, the more teaching to the test and the more cheating.  (http://nepc.colorado.edu/blog/houston-you-have-problem)

Value-added assessment is inherently incapable of producing better education because it does not measure better education. It only measures test scores. Higher test scores are a byproduct of better education. If you aim for the scores, you miss the target. The target is deeper understanding, greater knowledge, more thoughtful writing, more careful observation, a greater love of learning. The very act of measuring destroys the target instead of bringing it closer.