This paper contributes to the pedagogical discussion on how to promote critical thinking among adolescents in modern media environments. It argues that teachers play an essential role in guiding students' assessment of and decision between credible information sources. The study was carried out among eighth-grade health education teachers and students in a secondary school in Finland. Nexus analysis was used as a theoretical lens with which to analyze lesson observation data and teacher interviews. The findings indicate that teachers moved fluently between the informational authority roles of a cognitive authority and a trustee. Moments of perplexity in which teachers were not able to act in these informational authority roles created tension in the classroom; however, they also promoted diversified learning.