Participatory media are commonly used in today's society for a variety of purposes. The credibility associated with these media is sometimes contested, and their acceptance into school practices has been debated. Focus group interviews with teachers and librarians in upper secondary schools in Sweden are used to investigate conceptions and experiences of activities involving the critical evaluation of participatory media, with a particular focus on Wikipedia. Three themes are addressed. The first concerns how the teaching of the critical evaluation of sources is organized and comanaged between teachers and librarians. The second describes educators' experiences of print versus digital media, and their worry because students have problems negotiating the information architecture of print media. The third theme deals with conceptions of the credibility of Wikipedia. Four conceptions of credibility are identified: credibility is associated with the control and stability of a source; it is considered to be strengthened when several sources support a claim; it is viewed as situational and partial, rather than absolute; and it is associated with a multiplicity of voices and democratic forms of production. These findings may be used to inform educational activities around credibility and authority in schools by raising self-awareness among educators of various ways to talk about the credibility of sources with both colleagues and students.