"Search theory suggests that early career job changes on balance lead to better matches that benefit both workers and firms, but this may not hold in teacher labor markets characterized by salary rigidities, barriers to entry, and substantial differences in working conditions that are difficult for institutions to alter. Of particular concern to education policy makers is the possibility that teacher turnover adversely affects the quality of instruction in schools serving predominantly disadvantaged children. Although such schools experience higher turnover on average than others, the impact on the quality of instruction depends crucially on whether it is the more productive teachers who are more likely to depart. The absence of direct measures of productivity typically hinders efforts to measure the effect of turnover on worker quality. In the case of teachers, however, the availability of matched panel data of students and teachers, enables the isolation of the contributions of teachers to achievement despite the complications of purposeful choices of families, teachers, and administrators. The empirical analysis reveals that teachers who remain in their school tend to outperform those who leave, particularly those who exit the Texas public schools entirely. Moreover, this gap appears to be larger for schools serving predominantly low income students, evidence that high turnover is not nearly as damaging as many suggest"--National Bureau of Economic Research web site.