Why Test Scores CAN'T Evaluate Teachers

From the National Education Policy Center. the entire post is well worth a read, here's the synopsis

The key element here that distinguishes Student Growth Percentiles from some of the other things that people have used in research is the use of percentiles. It's there in the title, so you'd expect it to have something to do with percentiles. What does that mean? It means that these measures are scale-free. They get away from psychometric scaling in a way that many researchers - not all, but many - say is important.

Now these researchers are not psychometricians, who aren't arguing against the scale. The psychometricians as who create our tests, they create a scale, and they use scientific formulae and theories and models to come up with a scale. It's like on the SAT, you can get between 200 and 800. And the idea there is that the difference in the learning or achievement between a 200 and a 300 is the same as between a 700 and an 800.

There is no proof that that is true. There is no proof that that is true. There can't be any proof that is true. But, if you believe their model, then you would agree that that's a good estimate to make. There are a lot of people who argue... they don't trust those scales. And they'd rather use percentiles because it gets them away from the scale.

Let's state this another way so we're absolutely clear: there is, according to Jonah Rockoff, no proof that a gain on a state test like the NJASK from 150 to 160 represents the same amount of "growth" in learning as a gain from 250 to 260. If two students have the same numeric growth but start at different places, there is no proof that their "growth" is equivalent.

Now there's a corollary to this, and it's important: you also can't say that two students who have different numeric levels of "growth" are actually equivalent. I mean, if we don't know whether the same numerical gain at different points on the scale are really equivalent, how can we know whether one is actually "better" or "worse"? And if that's true, how can we possibly compare different numerical gains?

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Stop Saying That

When the governor of my state announced his plan for a new school funding formula, he said, "this is not about teachers, this is about the students." I wish he, and others, would quit saying that.

We hear this refrain almost every time there is an announcement about school reform or funding. It is meant to send a message: teachers do not care about kids.

I had hoped that after Newtown, with teachers selflessly giving their lives for their students, the 'teachers don't care' mantra would stop. Wrong again.

But here is the deal: this type of rhetoric is not only unhelpful, it is just plain wrong.

First, rhetoric like this does not help. We never hear it about other public policy debates. (Imagine: "This farm bill is not about farmers, it is about cows.") I cannot for the life of me figure out why policy makers think teachers are the enemy when it comes to education reform.

It might be that what they really mean is that this is not about the teacher unions. But that approach is incorrect as well. As a veteran administrator, I can assure you that there has not been any proof that non-unionized teachers do better in helping students achieve than those who are unionized. What does matter is how well teacher are supported in doing their jobs, and it's that support that teachers unions fight for.

The real problem with the idea that education reform and budgets are 'not about teachers' is this: if you want students to succeed, any reform must include teachers.

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