We report a study of a class of 28 sixth graders engaged in an extended computer-supported argumentive discourse activity. Participants collaborated with a same-side peer in arguing against successive pairs of peers on the opposing side of an issue. Meta-level awareness was facilitated by conducting the dialogs via instant messaging software, which made available a transcript of the dialog that was used in additional reflective activities. In the course of dialogs on 3 successive topics, participants showed significant gains in meta-level communications about the discourse, reflecting at least implicit understanding of its goals, as well as in the strategic moves that constituted the discourse. The latter advances remained evident when the social support of a same-side partner was withdrawn.