In upper tertiary educational programmes around the world, the new Web-mediated communication practices termed Web 2.0 are introduced as learning activities with the goal of facilitating learning through collaborative knowledge construction. The aim of this paper is to point to discrepancies in the views of learning, knowledge, and the goals of the practice implicit in Web 2.0 and educational practices and to argue that these discrepancies lead to theoretical tensions and practical challenges when Web 2.0 practices are utilized for educational purposes. The article is structured into four main parts: First, Web 2.0 is characterized from a practice perspective. Second, some conceptual discrepancies between the "practice logics" of Web 2.0 and educational practices are identified. Third, the question of transcending the discrepancies is raised through a discussion of related pedagogical strategies. Fourth, it is argued that the conceptual discrepancies bear out in practice as concrete challenges concerning collaboration, evaluation, and the general aim and status of the material produced by students. These challenges are illustrated with examples from the author's practical experience with Web 2.0-mediated learning activities in eight courses at the BA and MA levels.