This talk introduces a series of collaborative activity designs aimed at supporting student learning of mathematics in secondary school classrooms equipped with a local network of handheld devices. In designing learning activities, I use classroom networking tools to distribute resources and responsibilities for collective action, and to create conditions for productive interaction and equitable participation within student groups. A fundamental principle underlying each of these designs involves using network links among student devices as resources for emphasizing relationships among mathematical objects. Control of linked virtual objects is distributed among learners in configurations that reflect important links among mathematical phenomena, such as the relations among different representations of a function or the collective definition of a curve by a set of points. These networked social and mathematical relationships are intended to serve as resources to support learners as they jointly navigate the terrain of key conceptual domains. Drawing on results from an ongoing series of design-based research studies, I will describe several approaches to studying collaborative learning processes and classroom interactions in the context of these novel tools.