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Many school administrators, parents and policy makers advocate on behalf of improving the quality of teaching, but there is much debate over how best to do it. One method of evaluating teachers is based on students’ test scores, commonly referred to as the “value added” (VA) approach. But there are two fundamental questions about this approach. First, does VA accurately measure teachers’ impacts on scores or does it unfairly penalize teachers who may systematically be assigned lower achieving students? Second, do high VA teachers improve their students’ long-term outcomes or are they simply better at teaching to the test?
In a new research paper, “The Long-Term Impacts of Teachers: Teacher Value-Added and Students’ Outcomes in Adulthood,” authors John Friedman, Harvard Kennedy School (HKS), Raj Chetty, Harvard University and Jonah Rockoff, Columbia University address these questions. The researchers track one million children from a large urban school district from 4th grade through to adulthood. They also analyze whether high VA teachers also improve students’ long-term outcomes.
“We find that when a high VA teacher joins a school, test scores rise immediately in the grade taught by that teacher; when a high VA teacher leaves, test scores fall,” write the authors. Furthermore, “students assigned to higher VA teachers are more successful in many dimensions. They are more likely to attend college, earn higher salaries, live in better neighborhoods, and save more for retirement.”
The authors conclude that their study shows that great teachers create great value and that test score impacts are helpful in identifying such teachers. However, they say that more work is needed to determine the best way to use VA for policy.
John Friedman is assistant professor of public policy at Harvard Kennedy School. His research has focused on healthcare and tax policy, as well as the drivers and implications of redistricting. He is a Faculty Research Fellow at the National Bureau of Economic Research.