While the use of collaborative peer editing is widespread in some online learning contexts, little is known about how constituent editing behaviours impact student writing quality when using shared online documents as the mediating tool. Therefore, the present study (n = 176) examines the effects of English language learners' peer editing behaviours (comments and track changes) within the Google Docs platform on their subsequent academic writing quality at both individual and group levels. To better understand peer editing, the current study further divided track changes into either adding words or deleting words. Given the data's complexity, a two-level correlation analysis was used. The results showed that, at the individual level, words deleted by editors were positively associated with students' individual writing quality in the Introduction section. Further, words added by editors in the Introduction section were negatively associated with student individual writing. At the level of the peer editing group, there was a positive statistically significant correlation between words added and student writing quality in the Introduction and Discussion sections. Interestingly, comments had little association with student writing at the individual or group level.