Students’ engagement is an essential factor for the successful implementation of peer response in L2 writing. This qualitative study aimed to explore university students’ engagement in peer response activities and its influence on the revision and writing quality in enhancing and transforming blended learning environments. The subjects of the study were eight university students enrolled in two academic English writing courses. Data collection instruments included the recordings of peer response, students’ writing drafts, classroom observations, and reflective journals. The recordings of peer response were analyzed using Language Related Episodes (LREs), and the students’ drafts were scrutinized for revision and scored for writing quality. Data from the classroom observations and reflective journals were qualitatively analyzed. The main findings of the study are as follows. The students in both environments were actively engaged in peer response; however, the students in transforming blended learning showed more in-depth engagement in the discussion of writing topics. Second, the comments from peer response were incorporated into the revision. Last, the students’ second and final drafts gained higher scores than the first drafts. Based on the main findings, pedagogical implications are provided.