It is difficult these days to ignore the message that education matters. Governments everywhere in the world have assumed a substantial role in educating their citizens, and "providing education for all" is a central pillar of the Millennium Development Goals. A variety of motivations lead societies to provide strong support for schooling. Some are purely economic, while others are driven by ideas of using education to improve political participation, social justice and, more generally, develop society. The enthusiasm for promoting more education is well-warranted, but the fundamental question is how much society should invest, as public investment in education comes at the expense of other public and private investments. Analysis of the costs and benefits of school reform clearly shows investments that improve the quality of schools offer exceptional rewards to society. What is much less clear, however, is how to improve the quality of education.