Although prior studies have suggested the benefits of a collaborative approach to providing peer feedback in EFL writing, little is known about how students engage in collaborative peer feedback (CPF) activities. This paper reports on a case study involving five Chinese EFL students who collaboratively provided feedback on five argumentative essays written by their peers. We examined the CPF results generated by the students and found that they paid more attention to content-related issues and that negative feedback was more frequent than positive feedback. We also investigated the steps that the students took during CPF and the collaboration skills that they adopted. This revealed a four-step CPF procedure that included initiation, planning, deliberation and summarisation. Furthermore, our analysis showed that the students effectively used six of the nine social process skills in the framework of Hesse et al.: action, interaction, task completion, adaptive responsiveness, negotiation and responsibility initiative. However, the other three skills, namely audience awareness, self-evaluation and transactive memory, were not sufficiently applied. We suggest that EFL teachers integrate CPF into writing classrooms to enhance students' peer feedback performance. To enable successful CPF, teachers should help develop their students' collaboration skills.