This article provides a historical interpretation of one of the defining features of modern schooling: grades. As a central element of schools, grades--their origins, uses and evolution--provide a window into the tensions at the heart of building a national public school system in the United States. We argue that grades began as an intimate communication tool among teachers, parents, and students used largely to inform and instruct. But as reformers worked to develop a national school system in the late nineteenth century, they saw grades as useful tools in an organizational rather than pedagogical enterprise--tools that would facilitate movement, communication and coordination. Reformers placed a premium on readily interpretable and necessarily abstract grading systems. This shift in the importance of grades as an external rather than internal communication device required a concurrent shift in the meaning of grades--the meaning and nuance of the local context was traded for the uniformity and fungibility of more portable forms.