Introduction: This study concerns students' criteria in the evaluation of Internet sources for a school assignment requiring reflections on a controversial issue. The findings are elaborated by analysing students' discursive accounts in justifying the use or non-use of sources. Method: The interview data was collected in a Finnish upper secondary school during classes on religion and ethics. Thirty-nine students were interviewed in one to three person groups after they had given the presentation in the classroom. Analysis: The interviews were analysed using the discourse analysis in social psychology approach. The analysis concerned how different accounts related to information evaluation are used to justify the truthfulness of knowledge. Results: The most used evaluation criteria were the authority and neutrality of information. Various types of evaluation criteria and arguments were used simultaneously. The arguments were, in part, comparable to evaluation criteria presented in previous research. Conclusion: The evaluation criteria are cultural objects that can be utilized in various ways within different discursive contexts. The criteria were used in students' accounts alternately, not as mutually exclusive. Personal interests and high motivation with regard to the school assignment's subject were essential for students to identify and use more reflective and diverse argumentation related to evaluation criteria.