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Comment by Caroline M. Hoxby

In the United States, serious concern has arisen about out-of-field teaching among elementary and, especially, secondary teachers. While long-standing, it has been on the short list of key education issues since the publication of A Nation at Risk, twenty years ago. ³⁷ Concern about out-of-field teaching is currently so great that the No Child Left Behind legislation promulgated in 2002 contains strong incentives for schools to eliminate it. (These incentives fall under the "Highly Qualified Teachers" section of Title I.)

Richard M. Ingersoll does not address the question of whether out-of-field teaching has a negative effect on student achievement. Answering this question convincingly is extremely difficult because schools are not randomly assigned to have out-of-field teachers. It is easy to think that one is looking at the effects of out-of-field teaching when one is merely looking at the effects of the correlates of out-of-field teaching. Thus far, no credible evidence has been published about the causal effects of out-of-field teaching, and this is problematic. Education researchers must rely on their common sense, which suggests that teachers are unlikely to be effective if they have little or no formal education in the subject they teach. Nevertheless, in reading Ingersoll's paper, one must keep in mind that the effect of out-of-field teaching remains unknown. The supposition that it is negative is based on introspection and correlational data that do not reveal causal effects. Because school administrators should logically react to the effects, not the negative appearance, of out-of-fielding, one should always be mindful that no understanding has been reached about those effects when evaluating administrators' management of their teacher work force.

The Deficit Hypothesis and the Organizational Hypothesis

All this is by way of introduction to Ingersoll's paper, written by a leading scholar who accounts for much of the existing knowledge about the prevalence of out-of-field teaching. Ingersoll attempts to explain why out-of-field teaching takes place by examining the circumstances of schools that do and do not practice it. He describes two hypotheses about why out-of-field teaching occurs: the deficit hypothesis and the organizational hypothesis. He shows that no obvious evidence exists to support the deficit hypothesis. This is a very important finding because the deficit hypothesis is thought to be so obviously correct that it does not need to be debated. The deficit hypothesis dominates education schools and policy circles. By showing that it is probably not correct, Ingersoll opens the door for the organizational hypothesis. He also offers some direct evidence that the organizational hypothesis is correct, but the latter evidence must be described as suggestive instead of causal.

Essentially, supporters of the deficit hypothesis argue that out-of-field teaching is the result of too few prospective teachers being trained in a subject area. Also, they argue, teacher pay is too low generally, and this leads to teacher shortages. The consequence of the shortages is that schools fill vacancies with underqualified teachers—specifically, teachers who may be certified or prepared in an area but who are not certified or prepared in the field to which they are assigned.

In contrast, supporters of the organizational hypothesis argue that plenty of prospective teachers are certified in subject areas, but school districts mismanage their resources so that they end up assigning teachers to classes in which their subject area knowledge is slight. Such mismanagement may occur because administrators have weak incentives to manage their teaching staffs well or because districts may face high costs (in particular, costs associated with labor unrest) of changing rigid work rules or salary contracts to attract qualified teachers. Consider a district that attempts to rewrite its teachers' contract so that teachers who have math or science skills get paid a substantial premium for filling math and science assignments in secondary schools. (Math and science skills are...