The paper by Clotfelter, Ladd, and Vigdor examines the impact of teacher-student matching on the assessment of teacher effectiveness, using administrative data from North Carolina public schools. The authors find that highly qualified teachers are more likely to be assigned to advantaged students, leading to biased estimates of the effects of teacher qualifications on student achievement. To address this bias, they restrict their analysis to schools with randomly assigned students and find significant returns to teacher experience and licensure test scores in math and reading. They also observe that the returns to teacher experience are greater for socioeconomically advantaged students, suggesting that the observed patterns of teacher-student matching may be equilibrium outcomes. The study highlights the importance of considering non-random sorting in educational research and provides evidence on the policy-relevant behavior of teacher-student matching.The paper by Clotfelter, Ladd, and Vigdor examines the impact of teacher-student matching on the assessment of teacher effectiveness, using administrative data from North Carolina public schools. The authors find that highly qualified teachers are more likely to be assigned to advantaged students, leading to biased estimates of the effects of teacher qualifications on student achievement. To address this bias, they restrict their analysis to schools with randomly assigned students and find significant returns to teacher experience and licensure test scores in math and reading. They also observe that the returns to teacher experience are greater for socioeconomically advantaged students, suggesting that the observed patterns of teacher-student matching may be equilibrium outcomes. The study highlights the importance of considering non-random sorting in educational research and provides evidence on the policy-relevant behavior of teacher-student matching.