Online discussions offer exciting potential for educational dialogue, but too often result in disjointed conversations with low levels of interactivity. One contributing cause is the traditional text-based interface, which presents posts in a long list, leaving students overwhelmed and without useful navigational cues. To address this problem, we used information visualization techniques to design a graphical discussion forum interface. "Starburst" presents discussion posts as a dynamic hyperbolic tree: higher-level posts initially appear as larger and more central nodes, with each level of replies appearing smaller and more towards the periphery. To evaluate the new interface, students' discussion participation using "Starburst" was compared to their activity interacting with the same discussion content in a traditional text-based linear forum. Results showed that students were more purposeful in selecting which discussion threads to read when using "Starburst" and read new posts in a more connected fashion. Implications for the future design, use, and research of online discussions are considered.