This book examines the historical development of age-graded classrooms, a defining feature of modern public education that became embedded in the "grammar of schooling"--the fundamental organizational structures that shape how schools operate. Focusing on the implementation of gradation in New York City, the study traces the transformation of an urban school system from the nineteenth to the early twentieth century. Using actor-network theory as its analytical framework, the book explores how gradation emerged through complex assemblies of human and non-human actors along with the practical challenges of implementing graded systems, the educational concepts that supported these changes, and the administrative innovations required to manage increasingly complex school systems. Drawing on extensive archival research, this work illuminates how the age-graded classroom became a foundational element of US-American public education in rapidly growing urban centers.