The ability to write clear, correct proofs is a central goal of the curriculum for undergraduate mathematics majors. In an earlier study Moore (under review) investigated the proof-grading practices of four mathematics professors and showed that these professors devote much time and effort to reading students’ written proofs and marking the papers with corrections and suggestions for improvement. To learn how students interpret and make use of such feedback, we interviewed eight advanced mathematics undergraduates and asked them to respond to professor comments on three or four written proofs. The participants were asked to interpret and justify each comment and then write a revised version of each proof. Using the theoretical frameworks of communities of practice and legitimate peripheral participation, we analyzed the interviews and written data, compared the students’ interpretations of the comments to expert consensus, and identified patterns and commonalities in their responses and actions. A noteworthy finding was that even though students were able to identify and correctly implement the professor’s recommended changes, they sometimes misinterpreted the professor’s intentions.