The mantra of the current school reform movement in the U.S. is that high quality teachers produce high achieving students. As a result, we should hold teachers accountable for student outcomes, offering the most effective teachers bonus pay and shoving the least effective ones out the door. Of course, in order to implement such a policy you need a valid and reliable measure of teacher quality, and the reformers have zeroed in on one such measure, which is known as the value-added approach. According to this method, you calculate the effectiveness of individual teachers by the increase in test scores that students demonstrate after a year in their classroom.
Propelling this trend forward is a flood of research purporting to show that differences in teacher quality can lead to huge differences in the outcomes of schooling, both for students and for society. For example, in a 2010 study for the National Bureau of Economic Research, Eric Hanushek argues that a strong teacher by the value-added measure (one standard deviation above the mean) might raise the lifetime earnings of a student by $20,000. From this perspective, improving the quality of teaching promises to increase individual opportunity for the disadvantaged, which will reduce social inequality, and at the same time to increase human capital, which will promote economic growth and national competitiveness. Sounds great. Of course, this calculation is based on the assumption that test scores measure the economically useful knowledge of the future worker, which is far from obvious. But arguments like these provide a big incentive to generate actionable data on who’s a good teacher and who’s not.
All of this makes the current effort to develop a simple and statistically sound measure for good teaching quite understandable. But that doesn’t make it justifiable. The problem with this approach is that teaching is in fact an extraordinarily complex and demanding form of professional practice, whose quality is impossible to capture accurately in a simple metric. The push to develop such a metric threatens to reduce good teaching – and good education – to whatever produces higher scores on a standardized test. As a result, the value-added measure of teacher quality may end up promoting both the wrong kind of teaching and the wrong kind of schooling.
In this article, I explore three major questions that arise from this development. Why did the value-added measure of teaching emerge at this point in the history of American education? What are the core characteristics of teaching as a professional practice that makes it so hard to perform effectively and so hard to measure accurately? And under these circumstances, what are the likely consequences of using the value-added measure of teaching?