The goal of dialogue practice for a second language learner is to facilitate their production of dialogue similar to that between native speakers. This paper explores the characteristics of student and tutor dialogue in terms of their differences from classic conversational and task-oriented corpora. Interlocutors have the tendency to align to the language of the other in conversational dialogue, creating a symmetry between speakers which learners of a language may be unable at first to achieve. Our hypothesis is that as a learner's competence increases, symmetry between learner and tutor language increases. We investigate this at both a surface and a deeper level, using automatic measures of linguistic complexity, and dialogue act analysis. The data supports our hypothesis.