This paper explores the role of co-expressivity of drawing, speech, and gesture as sixth graders strive for intersubjectivity in their attempts to communicate solutions of a spatial reasoning task. Several obstacles to intersubjectivity are documented, particularly conflicts between a literal and geometric interpretation, limits of students' drawing abilities, and lack of conventions for designating cuts and interpreting three-dimensional information depicted in two dimensions. A conversation analysis approach reveals how failure to achieve intersubjectivity leads students to employ co-expressive forms of communication and to make conversational and representational repairs. The discourse analysis exposes students' optimistic views that their graphical representations will be understood by and convincing to others. It raises questions about the nature of students' understanding and production of graphical representations. Students need to see external, graphical representations as formal representations of the world. As such, they need to establish conventions for reading these representations and for connecting these representations with those aspects of the world they are meant to model. (Contains 4 figures.) [The research reported in this paper was supported by Interagency Education Research Initiative (IERI; a collaboration of NSF, Department of Education-OERI/IES, and NIH-NICHD).]