The Race to the Top (RTTT) Assessment Program has funded two state consortia to develop new assessment systems that measure student skills against a common set of college- and career-ready standards in mathematics and English language arts (U.S. Department of Education, 2010). The initial RTTT invitation to submit proposals prompted extensive discussion about a vision for next-generation assessment systems intended to play a critical role in supporting students to be college and career ready. To contribute to the vision, the Council of Chief State School Officers (CCSSO) published a white paper on comprehensive assessment systems to support high-quality learning. The paper called for assessment systems that supported multiple purposes at different levels of the educational enterprise and that included multiple forms of assessment, incorporating "formative as well as summative measures" (Darling-Hammond, 2010, p. 1). The thesis of this paper is that, despite the pioneering efforts of CCSSO and other organizations in the U.S., we already risk losing the promise that formative assessment holds for teaching and learning. The core problem lies in the false, but nonetheless widespread, assumption that formative assessment is a particular kind of measurement instrument, rather than a process that is fundamental and indigenous to the practice of teaching and learning. This distinction is critical, not only for understanding how formative assessment functions, but also for realizing its promise for our students and our society. The paper begins with a description of effective formative assessment and a clarification of some important distinctions that must be maintained if the benefits of formative assessment are to be achieved in our schools. These descriptions and distinctions introduce a brief consideration of the theory and research documenting the effectiveness of formative assessment. Next is discussion of the appropriation of formative assessment in a range of policy documents. The final section considers the role of formative assessment as part of a larger process of educational change. (Contains 2 footnotes.