Although education pays off handsomely in the United States, children from low-income families attain less education than children from more advantaged families. In this article, Cecilia Elena Rouse and Lisa Barrow investigate why family background is so strongly linked to education. The authors show that family socioeconomic status affects such educational outcomes as test scores, grade retention, and high school graduation, and that educational attainment strongly affects adult earnings. They then go on to ask why children from more advantaged families get more or better schooling than those from less advantaged families. For low-income students, greater psychological costs, the cost of forgone income (continuing in school instead of getting a job), and borrowing costs all help to explain why these students attain less education than more privileged children. And these income-related differences in costs may themselves be driven by differences in access to quality schools. As a result, U.S. public schools tend to reinforce the transmission of low socioeconomic status from parents to children. Policy interventions aimed at improving school quality for children from disadvantaged families thus have the potential to increase social mobility. Despite the considerable political attention paid to increasing school accountability, as in the No Child Left Behind Act, along with charter schools and vouchers to help the children of poor families attend private school, to date the best evidence suggests that such programs will improve student achievement only modestly. Based on the best research evidence, smaller class sizes seem to be one promising avenue for improving school quality for disadvantaged students. High teacher quality is also likely to be important. However, advantaged families, by spending more money on education outside school, can and will partly undo policy attempts to equalize school quality for poor and nonpoor children.