Whilst certain types of interactions between learners are potential vehicles for conceptual change, favouring production of such interactions in computer-mediated communication situations remains a difficult problem. We describe the CONNECT task sequence and interface for collaborative text writing, whose design aims to promote epistemic interactions involving argumentation and explanation with respect to fundamental domain concepts. Our approach involves pairing students according to semantic distance between their individual texts, encouraging expression of opinions on ideas in those texts, giving appropriate instructions on discussions, and partly structuring interactions. Within an iterative design approach, we present the results of a study in which students were asked to collaboratively write texts across the net on the interpretation of a sound phenomenon in physics. The interactions produced contained a high amount of explanation and argumentation, although communication management remained problematic.