This study explored 12 upper-intermediate and advanced learners' affective, behavioral, and cognitive engagement with peer feedback in TOEFL iBT preparation classes in an Iranian English-as-a-foreign-language context. The data were collected from textual analysis of original and peer-reviewed drafts of student writing, qualitative interviews, and focus group discussions. The analysis of the interviews showed that the learners' affective engagement with feedback was mostly negative because they tended to trust their teachers as reliable sources of grammar knowledge. However, this distrust toward peers was not observed for content-related feedback. Next, the analysis showed that the learners' negative affective engagement usually led to negative behavioral engagement with peer feedback, meaning that the majority of the learners did not review the provided peer feedback on grammar-related issues. However, the content-related peer feedback was reportedly used in the peer-reviewed drafts. Also, the learners who showed positive behavioral engagement with feedback tended to report positive cognitive engagement (e.g., allocation of attentional resources) with it, as well. Finally, the analysis of the differences between the original and peer-reviewed drafts showed that peer feedback potentially resulted in significant improvements in the quality of student writing. These improvements were, however, limited to content-related and word choice issues.