This book reports the analyses and recommendations of a study group formed by the National Research Council to develop conceptual guidelines that make content the driving force in mathematics assessment reform and to explore a variety of related measurement and policy issues. The document focuses on three principles that underlie effective educational assessment: the content principle, the learning principle, and the equity principle. Chapter 1 presents a vision of school mathematics as described in the current reform movement. Chapter 2 discusses the role of assessment in reform and proposes the three principles of assessing mathematics learning. Chapters 3-5 examine the impact that the principles have on the design of mathematical assessments, the learning that takes place in the classroom, and in supporting equal opportunities for all children to learn mathematics. Chapter 6 discusses how to evaluate educational assessments. The remainder of the book is comprised of three commissioned papers: (1) "Effects of Mandated Testing on Instruction" (Lynn Hancock and Jeremey Kilpatrick); (2) "Design Innovations in Measuring Mathematics Achievement" (Stephen Dunbar and Elizabeth Witt); and (3) "Legal and Ethical Issues in Mathematics Assessment" (Diana Pullin). Reference lists accompany each chapter and paper. A policy brief under a separate cover contains a summary of the main document. (MDH)