The debate about teacher quality owes a lot to the work of Stanford economist
Eric Hanushek. Almost every major paper and policy report on the topic cites his work.
Hanushek began studying teachers in the late 1960s. He was trying to understand what it is about schools that have an impact on how much students do — or don't — end up learning. He discovered that, of all the things that schools control, teachers matter most. More than class size, more than the curriculum, more than the amount of money spent per student. The best teachers get three times as much learning out of their students as the worst teachers, according to Hanushek's research.
It may seem obvious that teachers make a big difference. Students spend most of their day with teachers, and schools spend most of their money on teachers. Education is a teacher-driven business.
But for a long time, almost no one was talking about "teacher quality." The debate about teachers focused on qualifications: are they certified? Do they have master's degrees? Yet it turns out that teachers who have such credentials aren't necessarily better than teachers who don't.
What educators, researchers and policymakers talk about now is teacher "effectiveness." They look at how much students learn in each teacher's classroom by tracking test scores. That's what economist Eric Hanushek started doing 40 years ago, but back then he could only get his hands on a limited amount of test score data. Now, thanks to the proliferation of state testing and the federal No Child Left Behind Law, there is a vast supply of test score data for researchers to evaluate.
This trove of data is helping fuel research on teacher quality in American schools. The research, in turn, has made teacher quality one of the hottest topics in education policy debates.