The present study has two goals: to explore elementary students’ understanding of evidence and the ways they deploy it to construct arguments, and to examine whether eliciting their concept of evidence during argumentation improves students’ evidence-based reasoning. Individual semi-structured interviews were conducted with 4th and 6th graders in a public school in Mexico. We found significant differences between groups regarding the concept of evidence, with better performance in the older group. A positive correlation between the concept of evidence and the (...) quality of evidence-based reasoning was found. Also, three performance profiles were observed after eliciting the concept of evidence when grade was excluded as a factor. Results suggest that the concept of evidence plays an essential role in developing argumentative competence in pre-adolescence. (shrink)