Participating in discussions of classroom video can support teachers to attend to student thinking. Central to the success of these discussions is how teachers interpret the activity they are engaged in--how teachers "frame" what they are doing. In asynchronous online environments, negotiating framing poses challenges, given that interactions are not in real time and often require written text. We present findings from an online course designed to support teachers to frame video discussions as making sense of student thinking. In an engineering pedagogy course designed to emphasize responsiveness to students' thinking, we documented shifts in teachers' framing, with teachers more frequently making sense of, rather than evaluating, student thinking later in the course. These findings show that it is possible to design an asynchronous online course to productively engage teachers in video discussions and inform theory development in online teacher education.