Just how much does teacher quality matter? Quite a bit, according to a new Harvard University study of 2.5 million kids over 20 years. The researchers, Raj Chetty and John Friedman of Harvard and John Rockoff of Columbia University, find effective teachers are linked not only to better academic outcomes for students but also many other positive life outcomes.
“Replacing a teacher whose true [value-added] quality is in the bottom 5 percent with one of average quality would generate cumulative earnings gains of $52,000 per student, or more than $1.4 million for the average classroom,” Chetty said.
It doesn’t stop with test scores. The study findings indicate students of better teachers “are more likely to attend college, earn higher salaries, live in better neighborhoods, and save more for retirement,” Chetty said. “They are also less likely to have children as teenagers.”
Calculating Teacher Quality
The researchers used a “value-added” approach to measure teachers’ impact on students. The study, the largest ever to use value-added ratings, defined the “value” a teacher “adds” as the average test-score gain among his or her students, controlled for differences such as family income.
The study results indicate a significant impact on student achievement. For example, when a “high value-added (top 5 percent)” teacher begins at a school, student test scores increase immediately in the grade level that teacher teaches. Even having an average teacher instead of an ineffective one makes a significant difference, the researchers found.
“This study reinforces and extends the view that the quality of teachers is extraordinarily important,” said Eric Hanushek, a senior fellow at the Hoover Institution at Stanford University. “The findings show that it really matters how good teachers are, not just in terms of achievement scores but also in terms of life outcomes.”
Education Policy Implications
“If you leave a low value-added teacher in your school for 10 years, rather than replacing him with an average teacher, you are hypothetically talking about $2.5 million in lost income [for her students],” Friedman said.
Unfortunately, the U.S. education system is not structured to ensure the best teachers land and stay in the classroom, said Matthew Ladner, research director at the Foundation for Excellence in Education.
“The findings of this study strongly reinforce the need to reform the human resource practices of our public schools,” he said. “Teachers make an enormous impact on student learning gains and long term outcomes, but the typical American student continues to attend a school system barred from differentiating between effective and ineffective teachers.”
To ensure the best teachers fill U.S. classrooms, administrators should “make distinctions among teachers on the basis of their effectiveness,” Hanushek said. To retain the best teachers, he said, schools must reward them with greater pay and recognition and quickly remove poor teachers who damage students.
“All of this requires having a good evaluation system,” he said.
End of ‘Interchangeable Widgets’
The researchers set out to prove value-added assessments were worthless, Chetty said, and were surprised to find the opposite result and much more. A January report from the Gates Foundation likewise found value-added measures the most reliable method of assessing teacher quality.
Traditionally, unions have been among the greatest obstacles to such evaluation systems, objecting to policies that differentiate teacher performance. In 2011 several states, including Idaho, Indiana, New Jersey, Ohio, and Wisconsin, implemented policies to limit collective bargaining partly for this reason.
“The intellectual and moral isolation of the education unions will grow even greater if they continue to defend policies that treat teachers as interchangeable widgets rather than skilled professionals,” Ladner said.
Supporting quality teachers rewards educators and boosts the likelihood a child will have the best teacher possible, Hanushek said.
Failing to adopt policies that “ensure that all children have highly effective teachers implicitly says that student results are less important than the well-being of the adults in the schools,” Hanushek said.
“The Long-Term Impacts of Teachers,” Harvard University, December 2011: http://obs.rc.fas.harvard.edu/chetty/value_added.html
“Gathering Feedback for Teaching,” Gates Foundation, January 2012: http://www.metproject.org/downloads/MET_Gathering_Feedback_Research_Paper.pdf
Image by Chris Darling.