This paper argues that developments in collaborative e-learning dialogue should be based on pedagogically sound principles of discourse, and therefore, by implication, there is a need to develop methodologies which transpose -typically informal -models of educational dialogue into cognitive tools that are suitable for students. A methodology of 'investigation by design' is described which has been used to design computer-based dialogue games supporting conceptual change and development in

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... e -based on the findings of empirical studies. An evaluation of two dialogue games for collaborative interaction, a facilitating game and an elicit-inform game, has shown that they produce significant improvements in students conceptual understanding, and they are differentially successful -depending on the nature of the conceptual difficulties experienced by the learners. The implications this study has for the role of collaborative dialogue in learning and designing computerbased and computer-mediated collaborative interaction are discussed.