The research described in this paper investigates one possible explanation for students' ability or inability to identify fallacious arguments. As students' ability to identify informal reasoning fallacies has been the subject of scant empirical investigation, the current study may broaden our knowledge concerning this phenomenon and locate it in a wider context of epistemological understanding. We hypothesized that students' ability to identify invalid arguments (informal reasoning fallacies) in practice would be explained by their familiarity with argumentation norms. Two hundred and eighty-one middle and high school students were asked to perform informal reasoning fallacies and argumentation norms identification tasks. We compared performance on the fallacies task between students who were and were not familiar with the argumentation norms. The results provide strong support for our hypothesis by showing that students who were aware of general argumentation norms performed better in informal reasoning fallacies tasks.