Can the quality of teachers be measured the way that a person’s weight or height is measured? Some economists have tried, but the “value-added” they have attempted to measure has proven elusive. The results have not been consistent over tests or over time. Nevertheless, a two-part report by Raj Chetty and his colleagues claims that higher value-added scores for teachers lead to greater economic success for their students later in life. This review of the methods of Chetty et al. focuses on their most important result: that teacher value-added affects income in adulthood. Five key problems with the research emerge. First, their own results show that the calculation of teacher value-added is unreliable. Second, their own research also generated a result that contradicts their main claim—but the report pushed that inconvenient result aside. Third, the trumpeted result is based on an erroneous calculation. Fourth, the report incorrectly assumes that the (miscalculated) result holds across students’ lifetimes despite the authors’ own research indicating otherwise. Fifth, the report cites studies as support for the authors’ methodology, even though they don’t provide that support. Despite widespread references to this study in policy circles, the shortcomings and shaky extrapolations make this report misleading and unreliable for determining educational policy.

A response from the authors is below. Additional information on the study can be found at:
http://obs.rc.fas.harvard.edu/chetty/value_added.html

A further response from Moshe Adler follows below.