Research has shown that interactive engagement enhances student learning outcomes. A growing body of research suggests that the representations we use in physics are important in such learning environments. In this paper we draw on a number of sources in the literature to explore the role of representations in interactive engagement in physics. In particular we are interested in the potential for sharing disciplinary knowledge inherent in so-called persistent representations (such as equations, diagrams and graphs), which we use in physics. We use selected extracts from a case study, where a group of senior undergraduate physics students are asked to explain the phenomenon of refraction, to illustrate implications for interactive engagement. In this study the ray diagram that was initially introduced by the students did not appear to sufficiently support their interactive engagement. However, the introduction of a wavefront diagram quickly led their discussion to an agreed conclusion. From our analysis we conclude that in interactive engagement it is important to choose appropriate persistent representations to coordinate the use of other representations such as speech and gestures. Pedagogical implications and future research are proposed.