A new generation of networked classroom technology immerses students and teachers in the group-level construction of powerful mathematical and scientific concepts. We examine these networks from a sociocultural point of view as a new form of mediating artifact. We present a mixed-method, microgenetic analysis to characterize students' appropriation of mathematical content and practice as mediated by the Participatory Simulations system. Central findings of the study are that networked activities provided the opportunity for students and the teacher to: (a) act on multiple representations, (b) create collectively a linked set of mathematical objects that they could examine and discuss together, and (c) exercise agency in the production of mathematical discourse and practice. These opportunities fostered the development of powerful mathematical discourse. (Contains 5 figures, 2 tables and 3 footnotes.)