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Wednesday, March 11, 2009

Not Everyone Can Be in the Top Quartile

Dina wrote a very engaging dialog explaining how she might go about calculating her "teacher percentile", and why it is impossible with the data available.

And I realized what was the most bothersome thing about Bill Gates' recent bloviating about teacher quality. (Not, by a long shot, the only bothersome thing.)

He made this particularly asinine and ill-informed observation:

A top quartile teacher will increase the performance of their class -- based on test scores -- by over 10 percent in a single year. What does that mean? That means that if the entire U.S., for two years, had top quartile teachers, the entire difference between us and Asia would go away. Within four years we would be blowing everyone in the world away. So, it's simple. All you need are those top quartile teachers.

So simple!

Aside from all the other reasons it's not simple, Bill, your math is wrong.

You don't understand what a quartile is.

Take a group of people and measure something numerical about them. Their height, let's say. Take those heights and make a list of them from greatest to least. Cut that list into four equal sized chunks. The top chunk is the top quartile.

Surely everyone with half a brain notices the problem with his statement. We can't replace all the teachers with top quartile teachers. You only have a top quartile when you compare and rank the entire group. Only 25% of teachers can EVER be "top quartile". (Not to mention, say you buy this line of crap and go ahead and fire 75% of the teaching force. Where, exactly, is this magical pool of top teachers to replace them?)

You have to wonder what would happen if Bill got his wish. If 75% of working teachers were replaced with all these awesome, amaaaaazing teachers who are currently for some mysteeeerious reason not teaching. Do you think that after the first year he would realize that only 25% of the new group of teachers were top quartile? I picture him at his big Surface(tm) desk, pulling his hair, rubbing his temples, lamenting "How is this POSSIBLE?"

I thought he was supposed to be so smart...he should come sit in my 9th grade algebra class in a few weeks. That's when our Stats unit is. I will enjoy the moment when the kids realize they know more than Bill Gates.