We discuss student participation in an online social annotation forum over two semesters of a flipped, introductory physics course at Harvard University. We find that students who engage in high-level discussion online, especially by providing answers to their peers' questions, make more gains in conceptual understanding than students who do not. This is true regardless of students' physics background. We find that we can steer online interaction towards more productive and engaging discussion by seeding the discussion and managing the size of the sections. Seeded sections produce higher quality annotations and a greater proportion of generative threads than unseeded sections. Larger sections produce longer threads; however, beyond a certain section size, the quality of the discussion decreases.

NB is an in-place collaborative document annotation website targeting students reading lecture notes and draft textbooks. Serving as a discussion forum in the document margins, NB lets users ask and answer questions about their reading material as they are reading. We describe the NB system and its evaluation in a real class environment, where students used it to submit their reading assignments, ask questions and get or provide feedback. We show that this tool has been successfully incorporated into numerous classes at several institutions. To understand how and why, we focus on a particularly successful class deployment where the instructor adapted his teaching style to take students' comment into account. We analyze the annotation practices that were observed-including the way geographic locality was exploited in ways unavailable in traditional forums-and discuss general design implications for online annotation tools in academia.

Discussion forums are an integral part of all online and many offline courses. But in many cases they are presented as an afterthought, offered to the students to use as they wish. In this paper, we explore ways to steer discussion forums to produce high-quality learning interactions. In the context of a Physics course, we investigate two ideas: seeding the forum with prior-year student content, and varying the sizes of "sections" of students who can see each other's comments.

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