(Guest Post by Matthew Ladner)
Check it out. To do this right (aka as best we can) schools need to have multiple tests to get much more data and thus much less error. The state of the art with this involves teachers drawing up their own common assessment items based on state academic standards, giving monthly assessments, and tracking student learning gains together as departments. Teachers can own this process, and either remediate or weed out ineffective instructors themselves.
Fantasy? Nope- it is already happening, and it is not rocket science.
Even improved scores should also be only a (big) part of an assessment, and the goals should be communal as well as individual.
All this reactionary hand-wringing about the measures not being perfect is a waste of time. We need to get these measures as close to perfect as we can and then run with them. Stringing together three crappy state tests in a row is NOT as close to perfect as we can get, but it is much better than nothing.
I’m not willing to settle for better than nothing. Rock star pay for rock star teachers or bust baby!
Jay P. Greene's Blog 
Milton Friedman once said, if you can measure it, measure it; and if you can’t measure it, measure it anyway.
I’m glad that teacher performance falls into the former category and not the latter, but the point is still relevant.
Oh, and it’s universal vouchers or bust!
If you have a lot of time on your hands you can catch a young, buff Jack Black playing the villain in the Neverending Story 3 (a story that should have ended with the first movie).