-random distribution of teachers and students among classrooms within schools. We find compelling evidence that teacher credentials affect … distribution of teacher credentials by race and socio-economic status of high school students -- a pattern we also document …

availability of data on all teachers and students in North Carolina over a ten-year period allows us to explore them in more detail … effects of changes in class size or to the socio-economics characteristics of students, as measured, for example, by the … education level of their parents …

to be matched with more advantaged students, and we measure the bias this pattern generates in estimates of the impacts … restrict the analysis to schools that assign students to classrooms in a manner statistically indistinguishable from random … advantaged students, a finding that may help explain why the observed form of teacher-student matching persists in equilibrium …