Because prior beliefs can affect how people argue and respond to controversial claims, in this study we examined how patterns in students' responses posted in online debates were associated with students' initial positions on given claims prior to debate. Students that held initial opposing positions to the claim exhibited the tendency to respond to challenges from the opposition with explanations and to respond to explanations from the opposition with challenges. This response pattern was not observed among students with initial supporting and neutral positions. These findings suggest that manipulating group composition based on prior beliefs and manipulating the direction and phrasing of the claim under debate may help to elicit more frequent exchange of opposing viewpoints and raise the level of critical discourse.