The following discourse analysis examines the ways open-ended feedback, defined as dialogic, interpretative, and revisionary, fosters co-regulation and metacognition. Data come from a Writing in the Major course at a large land-grant institution in the Pacific Northwest. Students' written essays and reflections, both with teacher feedback included, were collected along with interviews with both students and teachers. Analysis focused on instances of interdiscursivity, when students incorporated their teachers' discourse into their revisions and reflections. The study suggests that open-ended feedback promotes opportunities for co-regulation and metacognition when students become active agents in the assessment process.