Advocates of distributed cognition argue that cognitive accomplishments rely in part on structures outside the individual mind - structures located in other minds or in artifacts that we think with. This paper argues that, in some cases, interactional structure can also make essential contributions to cognition. The data are transcribed classroom discussions, in which teachers and students use language to establish both referential and interactional patterns. The analyses use techniques from linguistic pragmatics, to uncover emergent interactional structure in the conversations and to show how this structure might make essential contributions to the cognitive value of those conversations.