Analyzing user behavior in electronic textbooks offers appealing insights into how pupils interact with the book and internalize the content. Using these insights may help to personalize the book, e.g., to support users with special educational needs. Conventional approaches often focus on atomic, user-triggered events like clicks or scrolls. In this paper, we propose to view all ongoing sessions in a classroom simultaneously and cast the problem as a multi-user problem over space and time. We devise two distance measures to compare the navigation behavior of pupils in different dimensions. Empirically, we observe that our metrics lead to interpretable clusters and serve as performance indicators. [For the full proceedings, see ED593090.]