This study investigated the use of a wiki for collaborative writing among primary levels five (P5) and six (P6) students (n = 119) in a Chinese primary school in Hong Kong where English is taught as a second language (L2). Three classes of students and their English subject teachers participated in a three-month English language writing programme using a wiki. Quantitative and qualitative data were analyzed from activities recorded in the wiki system, including posted edits and comments, students' group writings and student and teacher interviews. The wiki page history revealed information on the types of revisions that occurred, showing that different types of feedback elicited actual revisions, which may have resulted in better group writing. Findings from the study may shed light on how wikis can help provide support for students' collaborative writing process with wikis, and how peer-feedback can influence this process.