Evidence is widely recognized as an essential component of argumentation. Existing research has primarily focused on students' use of evidence to construct explanations or claims. In the present study, 54 11- to 12-year-old Chinese students participated in an extended discourse-based argumentation curriculum, along with an equivalent nonparticipating control group consisted of 50 students. We identified and traced progression in students' meta-talk about evidence during peer-to-peer argumentive discourse and found that meta-talk grew more frequent over time, became increasingly focused on evaluating the source of evidence, and became better sustained over successive turns. Separate pre- and postassessments suggested that participants had become more advanced in epistemological understanding, manifested in a shift away from absolutist thinking, and were more likely to endorse the values of argumentive discourse. Implications for epistemic vigilance in the Information Age are discussed.