Research shows teachers have a huge impact on how much students learn. Students who get the best teachers learn a lot, and students who get the worst teachers fall behind.
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.
Here is some of what researchers have learned:
- There are huge variations in teacher effectiveness. Some teachers are really good at getting their students to learn, and others are not.
- Teacher quality matters so much that a student is likely better off in a bad school with a good teacher than in a good school with a bad teacher.
- You can find ineffective teachers in good schools and effective teachers in bad schools. But struggling schools tend to have more ineffective and inexperienced teachers.
- African-American students may be particularly likely to get ineffective teachers. According to a study of two large school districts in Tennessee, black students were overrepresented in the least effective teachers' classrooms by about 10 percent. They were also under-represented in the most effective teachers' classrooms by 10 percent. This is from a study by researcher William Sanders, who has done a lot of pioneering work about teacher quality.
- Students of the most effective teachers make excellent academic progress regardless of their prior achievement levels, while students in the classrooms of the least effective teachers do not progress well.
- As the level of teacher effectiveness increases, the lowest–achieving students are the first to benefit.
- Having a high–quality teacher throughout elementary school can substantially offset or even eliminate the disadvantage of low socio-economic background. If poor children consistently got great teachers, the achievement gap could disappear.
- The effects of bad teaching last. Even if a student eventually gets great teachers, those who had ineffective teachers in the past continue to lag behind their peers. "Although an effective teacher can facilitate excellent academic gain in students during the years in which they are assigned to them," writes researcher William Sanders, "the residual effects of… ineffective teachers were measurable two years later, regardless of the effectiveness of teachers in later grades"