Low-performing teachers have high costs.

Hanushek, Eric A.

The movie Waiting for Superman chronicles the role of chance in determining the fate of a relatively small number of families trying to enroll their children in oversubscribed charter schools. Raj Chetty, John Friedman, and Jonah Rock-off document the much larger problem of ineffective teachers scattered about a multitude of schools. From the viewpoint of the student, this latter issue may appear to be chance when class assignments are made, and when some get good teachers and others get ineffective ones. From the standpoint of the system, however, it is not chance but mismanagement that allows ineffective teachers to continue harming students.

Chetty et al. have produced new and elegant estimates of how teacher effectiveness relates to longrun student outcomes. As economists are prone to do, they have produced a paper that deals with a long list of technical questions that have absorbed the scientific literature on teacher effectiveness. Their work is thorough, convincing, and scientifically innovative.

The overarching idea of the paper is linking gains from having a high-value-added teacher in grades 4-8 to subsequent long-run outcomes, including college attendance, earnings, and family creation. But, from the outset, they must deal with the two primary challenges leveled at teacher value-added measures based on student test scores. First, are these estimates biased measures of effectiveness? The answer is no. The wealth of information that Chetty et al. have about families from tax records and some clever analyses effectively rule out the possibility that conventional estimates of value-added based only on school administrative data are misleading. Second, do the effects of good teachers (or bad teachers) quickly fade away? Again, the answer is no. Even as these students leave school and enter into adult careers in their late 20s, the significant trace of their early schooling is quite discernible.

But the warranted attention to this work derives not from its technical aspects but from the policy implications of the results. The fundamental finding is that good teachers have an extraordinarily powerful impact on the future lives of their students. Symmetrically, the researchers show the lasting damage that poor teachers have on the lives of their students. This work sweeps away a variety of attempts to deflect questions about the importance of teacher quality and our ability to identify it. It also brings us back to the question of informed policy.

As the evidence on the importance of teacher quality has grown, policy discussions have actually moved. In the beginning, there were doubts about the impact of teacher quality relative to families, curriculum, or a host of other influences. Those doubts have largely receded and been replaced by questions of how policy should proceed. And here is where the additional evidence presented in the Chetty study comes into play.

Much of the discussion has centered on the political difficulties of reforming the schools by dealing with the problem of the most ineffective teachers. The unions have dug in their heels, resisting any change that does not ensure perfect identification of the worst teachers. Their resistance has resulted in many policymakers simply asserting that it is too politically costly to make active decisions about teacher effectiveness and instead looking to alternatives such as more professional development, better mentoring, or heightened requirements of certification.

Chetty et al.'s evidence shows that bad teachers cost hundreds of thousands of dollars in lost income and productivity each year that they remain in the classroom. These costs are large enough that failing to address them is simply inexcusable. It is time that we develop policies that truly are designed to help our children and not just the adults in schools today.

We have recently seen a number of brave states step out and legislate better evaluations of teachers including, when possible, the use of value-added measures. Coupled with both pay and tenure reforms, these movements show real promise and should be encouraged on a wider scale.

Eric A. Hanushek is senior fellow at the Hoover Institution of Stanford University.