The authors present a case study of a world history teacher's mediation of her students' world historical thinking and writing through unit-level cognitive tools. They analyze both scaffolding and disciplinary tools that the teacher constructed for her students in order to improve their world historical thinking, and the degree to which the students used these supports. Ms. Stark's World History classroom and her teaching provide an instructive case that highlights potential avenues for supporting the development of historical disciplinary literacy and gives insight into the challenges in helping students make sense of large amounts of time and space in world history. This article corroborates research on the challenges of using scaffolding tools to teach history and the complexity of teaching disciplinary literacy, and illustrates the importance of close examinations of how teachers scaffold student acquisition of important disciplinary tools that support their thinking and writing in history in general and world history in particular. (Contains 2 tables and 1 note.)