Peer feedback is often considered a critical component of self-regulated learning. The purpose of this mixed-method study was to understand the effects of how a unique form of peer feedback – an online system of co-construction – might both trigger and sustain self-regulation in academic writing. Participants were 21 Japanese undergraduate EFL writers, 10 of whom worked as peer advisors in an online writing center. Peer advisors self-reported significantly more strategies than the comparison group. In addition, textual analysis of the feedback that peer advisors provided to writers showed evidence of strategy internalization, whereas the comparison group lacked metacognitive awareness and provided feedback of a lesser quality. Within group analysis points to how specific characteristics of peer feedback developed over time and with experience. This study considers how educators can use online feedback-on-feedback as a method for eliciting verbalizations of self-regulation.