People without a background in argumentation theory possess several criteria to distinguish strong from weak arguments. The fact that people have these criteria does not imply that they will use them to objectively assess the quality of an argument. Research on motivated reasoning suggests that people take a more critical stance toward arguments that go against their opinions compared to arguments that are in accordance with these opinions. In this study, the question was addressed whether people employ criteria to evaluate arguments in a biased way. Forty participants were told that they would take part in a debate and either had to defend the claim that mixed schools (that is, schools attended by children with different ethnic backgrounds) were desirable or the claim that these were undesirable. All participants received sixteen (strong and weak) arguments and were asked to prepare themselves for the debate while thinking aloud. Analysis of the think aloud protocols showed that people almost exclusively used criteria to boost the quality of arguments supporting their claim while disqualifying arguments that went against it. These results provides important insights into the nature of motivated reasoning because they show how people deploy argument criteria in this process.