Why does the implementation of a CSCL tool result in desired effects in some classroom contexts and not others? Even when optimally designed, the CSCL tool is only a necessary component, not sufficient. The central challenge lies in creating the appropriate social infrastructure around the tool. Social infrastructure refers to the supporting social structures enabling the desired interaction between collaborators using the CSCL tool. In this paper we introduce and apply a framework for examining social infrastructure and its implications for CSCL tools. We extend our earlier theoretical work on learning communities (Bielaczyc & Collins, 1999; Collins & Bielaczyc, 1997) to examine the use of CSCL tools in building computer-supported learning communities. We focus specifically on a year-long study involving the use of KnowledgeForum by a 6th-7th Grade Team of teachers and students in a U.S. middle school. Over the course of the year, the teachers varied the ways that they used KnowledgeForum in the classroom, resulting in changes in the social infrastructure over time. We describe three specific patterns of use for KnowledgeForum, compare and contrast various features of the resultant social infrastructure, and discuss the implications for supporting learning communities.

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