The skill of argumentation is problematic for EFL students who are linguistically and rhetorically deficient in expressing academically appropriate forms in English. In fact, many EFL students struggle to write highly elaborate arguments. In this study, we investigated whether EFL students’ skills for argumentation improved after receiving peer feedback. We also investigated which elements of argumentation were related to the quality of argumentative writing. To this end, we used the Toulmin model of argumentation. We collected 34 EFL students’ first drafts and revisions as well as reviewers’ written feedback, and analyzed their drafts and revisions with a range of quantitative and qualitative approaches. We found that peer feedback had a positive effect upon overall writing quality. Peer feedback made meaningful contributions to the development of students’ argumentative strategies they employ. It seems apparent that peer response prompted the students to reflect on whether the logic of their argumentation made sense to the readers.