In a previous study we found that students receiving feedback from multiple peers improve their writing quality more than students receiving feedback from a single expert. The present study attempted to explain that finding by analyzing the feedback types provided by experts and peers, how that feedback was related to revisions, and how revisions affected quality. Participants were 28 undergraduates who received feedback from a single expert (SE), a single peer (SP), or multiple peers (MP), thus forming three groups, respectively. The MP group received more feedback of all types. Non-directive feedback predicted complex repairs that the MP group made more than both other groups. Complex repairs were associated with improved quality. (Contains 2 tables and 2 figures.)