Lisa Guisbond:

As a rookie mom, I used to be shocked when another parent expressed horror about a teacher I thought was a superstar. No more. The fact is that your kids’ results will vary with teachers, just as they do with pills, diets and exercise regimens.
Nonetheless, we all want our kids to have at least a few excellent teachers along the way, so it’s tempting to buy into hype about value-added measures (VAM) as a way to separate the excellent from the horrifying, or least the better from the worse.
It’s so tempting that VAM is likely to be part of a reauthorized No Child Left Behind. The problem is, researchers urge caution because of the same kinds of varied results featured in playground conversations.
Value-added measures use test scores to track the growth of individual students as they progress through the grades and see how much “value” a teacher has added.

The Madison School District has been using Value Added Assessment based on the oft – criticized WKCE.