Students of American politics rarely study public sector unions and their impacts on government. The literature sees bureaucratic power as rooted in expertise, but largely ignores the fact that bureaucrats often join unions to promote their own interests, and that the power of their unions may affect government and its performance. This article focuses on the public schools, which are among the most numerous government agencies in the country, and investigates whether collective bargaining by teachers—the key bureaucrats—affects the schools' capacity to educate children. Using California data, analysis shows that, in large school districts, restrictive labor contracts have a very negative impact on academic achievement, particularly for minority students. The evidence suggests, then, that public sector unions do indeed have important consequences for American public education. Whether they are consequential in other areas of government remains to be seen, but it is an avenue well worth pursuing.