Lunching today with one of my favorite educators, I remembered my basic Archimedean physics: "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world," he reportedly said.
The answer, I think, is that assessment changes instruction when it connects with a school's culture.
If teachers and leaders are collaborating in the right ways, operating as a professional learning community, they study the results, analyze the standards, and keep adjusting instruction to get move each student ahead.
If they aren't working together that way, the same test can lead to drill-and-kill reviews, excessive practice testing, and lots of external rewards for students who don't find any intrinsic value in their studies.
Rest the lever of sound assessment on the fulcrum of a collaborative learning-focused culture, and we will indeed move the world.