While previous research on peer feedback in l2 writing has stressed the importance of training in giving useful comments on peer’s writing, very few studies have specifically explored metacognitive training in peer review interaction in terms of the perception and actual reviewing practices of l2 learners. This mixed-methods study employed a 12-week intervention course in l2 writing, in which eighteen secondary one students, aged 12-13 years, received metacognitive training in peer review interaction. The training focused on metacognitive knowledge and metacognitive regulations. The results showed that, first, metacognitive training in peer review interaction helped change the perception of these young learners and increased their level of engagement and collaboration during the five peer review tasks. Second, metacognitive training appeared to encourage students to provide more content-related feedback than language-related feedback during dyadic interactions. Finally, it was found that the students were able to seriously consider their peer feedback when revising the peer-reviewed drafts, but written feedback had a much higher chance of being incorporated than did oral feedback. The pedagogical implications of these findings were discussed. University of antwerp.