This paper presents a higher education experience aimed at explicitly promoting metacognitive processes in a social and collaborative context. Students carried out a debate on an e-forum, and were later asked to collaboratively analyse their own debates. The control group conducted this analysis using text-based tools; the experimental group analysed it with a graphical tool ("DebateGraph"). We examine the consequences of such experiences in promoting students' metacognitive processes for argumentative competence, as well as its impact on content knowledge learning. The analysis yields different results depending on the perspective adopted: students' self-assessment or instructor's assessment.