Prometheus 6

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Student Demographics, Teacher Sorting, and Teacher Quality: Evidence from the End of School Desegregation
C. Kirabo Jackson, Cornell University

The reshuffling of students due to the end of student busing in Charlotte-Mecklenburg provides a unique opportunity to investigate the relationship between changes in student attributes and changes in teacher quality that are not confounded with changes in school or neighborhood characteristics. Comparisons of ordinary least squares and instrumental variable results suggest that spatial correlation between teachers’ residences, students’ residences, and schools could lead to spurious correlation between student attributes and teacher characteristics. Schools that experienced a repatriation of black students experienced a decrease in various measures of teacher quality. I provide evidence that this was primarily due to changes in labor supply.

I. Motivation and Introduction
Many education policy interventions, such as school vouchers, school choice, district consolidation, and student busing, change the student demographics of schools. Such policies are predicated, in part, on the hypothesis that it is helpful to reshuffle peers while keeping other things roughly the same. While this may be true, it may be impossible to keep teaching “roughly the same” if teacher quality is endogenous to student characteristics. Since salaries do not vary across schools within a district, teachers have little financial incentive to teach at undesirable schools. Since observably better teachers will be hired over weaker teachers and all teachers are likely to apply for the most desirable jobs, schools with undesirable working environments will have teachers of lower average quality. As such, if teachers prefer working environments with students of a particular demographic, teacher quality would be endogenous to student demographics and, ceteris paribus, students whom teachers find undesirable will be exposed to teachers of lower quality.With such teacher sorting, policies that change the composition of students may change the composition of teachers in unforeseen and undesirable ways. For example, the movement of high-quality teachers out of schools with growing black enrollment shares may be partially responsible for the ill effects of school segregation to black students documented by Guryan (2004) and Lutz (2005) and for the finding that higher black enrollment shares are associated with lower test scores (Hoxby 2000; Hanushek, Kain, and Rivkin 2004a).

Although research results are mixed, there is evidence that years of teaching experience, selectivity of undergraduate institutions, teachers’ test scores, and regular licensure are associated with higher student achievement (Brewer and Ehrenberg 1994; Hanushek 1997; Brewer and Goldhaber 2000; Clotfelter, Ladd, and Vigdor 2006, 2007; Anthony and Goldhaber 2007). Studies that identify teachers associated with student test score gains show that a one standard deviation increase in teacher quality leads to between one-tenth and one-fifth of a standard deviation increase in math and reading scores (Rockoff 2004; Hanushek, Kain, and Rivkin 2005; Aaronson, Barrow, and Sander 2007). Jacob and Lefgren (2008) find that principals’ subjective evaluations of teachers are highly correlated with subsequent increases in student achievement.

Researchers have found that high-poverty schools tend to have teachers with lower qualifications than low-poverty schools and that teachers tend to leave schools with low-achieving, poor, minority students, particularly when there are vacancies at schools with higher-achieving, affluent students. This evidence is based on observation of teacher attributes, or changes in teacher attributes, at schools whose student populations are unchanging or are changing because of unobserved factors that could also affect teacher labor supply. I provide an overview of the literature and discuss why, on the basis of previous studies, one cannot say whether the observed differences are caused by (a) school attributes that are correlated with student characteristics, (b) neighborhood attributes that are correlated with student characteristics, or (c) mobility of teachers toward their residences that happens to move them out of inner-city schools. Since previous studies have been unable to separate the effect of student characteristics on teacher quality from those of neighborhoods or schools, we have little knowledge of the direct relationship between student characteristics and teacher quality and little understanding of how policies that change the composition of students across schools might affect the distribution of teachers.