We examine how extended engagement in argumentation with peers leads to enhanced metalevel understanding of argumentive discourse. Following such engagement, young adolescents demonstrated enhanced understanding of counterargument and use of evidence as objectives of skilled argumentation, relative to a nonparticipating comparison group. Among the participating group, analysis of metatalk (talk about the discourse, distinguished from talk about the topic) during electronic peer dialogs proved revealing regarding participants' evolving awareness of and adherence to discourse norms. Metatalk became more reciprocal and sustained with time and revealed an increasing focus on the argumentation process and engagement in talk that seeks to direct it. Implications are considered for understanding and studying argumentation as a social practice that encompasses not only individual skills but also the less visible norms that govern it and that members of a social group come to share.