We propose mobile sensemaking as a collaborative mechanism to explore and understand information in highly mobile and fluid situations, where people engage in multiple parallel, rapid and ad-hoc interactions, rather than participating in large highly-structured decision processes. Mobile sensemaking is explored in the classroom context, where it has been recognized that the traditional lectures should be reconstructed as active processes centered on collaborative activities. Mobile sensemaking relies on mobile computing devices and a proximity model, both organizing collaborative activities according to the domain context and physical proximity. The paper describes in detail the proposed proximity model and the developed mobile application.