Although teacher commentary on student papers and students' revisions have been investigated separately, the relationship between commentary and revision has not been much studied. Such a gap in the research leaves the nature of the progression from effective commentary to substantive revision obscure. This article describes a mixed method study, using quantitative and qualitative data, that grew out of a WAC assessment project in which multiple drafts of 64 student papers from first-year composition and writing-in-the-disciplines courses were examined to measure the extent and kind of revisions made by students after receiving feedback from their instructors. We conclude that revisions--especially substantive revisions--correlate with comments that address substantive matters; we provide empirical data to support that finding; and we consider the role of individual teachers and their classroom practices in encouraging substantive revision.