Standards-based reform is a strategy that includes specifying what is to be learned, devising tests to measure learning, and establishing consequences of performance for students and schools. Popular support remains strong for standards-based reform, according to national polling data as well as local data in the states implementing this strategy. However, opposition has emerged in several states, in the run-up to full implementation of standards-based reforms. Objections fall into different categories. One source of discord concerns the content of what should be learned. This article presents the authors' theoretical and empirical analysis and review of standards in practice. The authors focus on disputes over testing and cutoff scores based on unresolved disagreements over content standards. The theoretical analysis shows that some problems alleged by critics of standards-based reform are not particularly compelling, notably those based implicitly on the logic of pooling and those concerning incentives for high-achieving students. But it also points to a trade-off between incentives for those lesser achieving students who will be stimulated to meet high standards and those low-achieving students who will be discouraged. Based on their knowledge of reform efforts in California, Massachusetts, and other states, and the theoretical and empirical research on standards, the authors identify four key obstacles that can stand in the way of higher educational standards: (1) opposition arising from concerns about the distribution of student achievement; (2) problems in defining standards and assessing students' progress toward those standards; (3) the need to align the incentives of all participants in public education; and (4) equity concerns created by the large gap in school resources that currently exists among students from various socioeconomic groups in some states. Comments by Herbert J. Walberg, Meredith Phillips, and Tiffani Chin are included. (Contains 5 figures, 4 tables, and 98 notes.)