My dissertation is composed of three essays on the economics of education. The first essay, "Teachers' Comparative Advantage, School Segregation, and Educational Mobility in Chicago Public Schools," co-authored with Lauren Sartain, examines a basic assumption that value-added (VA) models make. Specifically, this essay tests whether teacher effects are student specific. We develop and estimate a flexible multivariate VA model in which teacher effects can vary by student type and drift over time. Defining student type by race and using data on 1.7 million observations, we employ quasi-experimental and holdout strategies that exploit teacher switching in Chicago Public Schools. We find evidence of student-specific teacher effects, thus reject...