Both formative and summative assessment in online discussion-based courses have typically focused on the behavior of individual students. Metrics such as the number of posts or number of words are typical. While these metrics are arguably a reasonable proxy for the efforts of individual students, they give little insight into how successfully students are engaging with either the material or their peers. By using social network analysis to focus on student interactions, instructors can get better information about which students require additional support and can also meaningfully assess students' contributions to the knowledge building enterprise at the heart of constructivist pedagogy.