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 true in teacher labor markets characterized by salary rigidities, barriers to entry, and substantial differences in working conditions that are difficult for institutions to alter. Education policy makers are particularly concerned that teacher turnover may have adverse effects on the quality of instruction in schools serving predominantly disadvantaged children. Although these schools experience higher turnover, on average, than other schools, the impact on the quality of instruction depends on whether more productive teachers are more likely to depart. In Texas, the availability of matched panel data of students and teachers enables the isolation of teachers' contributions to achievement despite the intricacies of the choices of families, teachers, and administrators. Teachers who remain in their school tend to outperform those who leave, particularly those who exit Texas public schools entirely. This gap is larger for schools serving mainly low income students--evidence that high turnover is not nearly as damaging as many suggest. Correspondence Between Assignment into Sorted and Not-sorted Categories by Test Statistic is appended. (Contains 13 tables, 2 figures and 25 footnotes.)