Wikis have been recently promoted as tools that foster collaborative learning. However, there has been little research devoted to the criteria that are suitable to address issues pertinent to collaborative learning. This paper proposes a set of criteria to explore technical and pedagogical usability issues of collaborative learning with wikis. The criteria are then used to evaluate students' collaborative writing activities. The units of study are wikis that groups of students developed collaboratively using MediaWiki. This paper also reports on technical and pedagogical implications for the use of wikis as collaborative learning tools in teacher education.