After decades of narrowing, the achievement gap between black and white school children widened in the 1990s--a period when the labor market rewards for education were increasing. This presents an important puzzle for economists. In this chapter, I investigate the extent to which economic models of segregation, information-based discrimination, peer dynamics, and identity can explain this puzzle. Under a reasonable set of assumptions, models of peer dynamics and identity are consistent with the time-series data. Segregation and models of discrimination both contradict the trends in important ways.