This paper is concerned with the question of how activity mediated by shared representations-notations that are manipulated by more than one person during a collaborative task-might constitute knowledge construction activity. The paper begins with a brief review of theoretical perspectives on how representations mediate collaborative knowledge construction, to identify the kinds of events we would look for as evidence of knowledge construction in via a representational medium. Then the paper draws on data from a prior study in which participants collaborated via a graphical representation as well as a verbal "chat" tool, to identify instances of such events and illustrate ways in which the activity of two individuals can be coupled and joined into a larger cognitive (and sometimes knowledge construction) activity distributed across the persons and representations they are manipulating.