Wiki technology provides new opportunities to foster collaborative learning in various educational settings. To empirically examine the impact of wikis on learning, this article explores students' collaborative writing activities performed on MediaWiki. The activities were analyzed using a taxonomy with ten categories (clarify content, add content, delete content, add link, delete link, fix link, grammar, spelling, style/typography, and formatting). The work also analyses students' comments posted on the discussion page of the wiki. The results show important differences in the types of contributions across the categories investigated. The results also reveal that the level of collaboration and discussion was relatively low compared with other activities performed on the wiki. Finally, the article suggests a number of factors influencing wiki-based collaborative writing in teacher education. (Contains 3 tables.) [For the complete proceedings, "Proceedings of the International Association for Development of the Information Society (IADIS) International Conference on Cognition and Exploratory Learning in Digital Age (CELDA) (Madrid, Spain, Oct 19-21, 2012)," see ED542606.]