Social networking sites may include argumentative writing about particular issues in which participants adopt competing perspective and discourses on those issues. This study examined roles and discourses adopted by high school students participating in an online role-play conducted on a Ning platform regarding their school's Internet policies on open access to websites. Analysis of discourses voiced by students engaged in collaborative arguments found that tensions between competing discourses resulted in students' challenging each other's as well as their own perspectives on the issue. Recognizing these competing discourses enhanced students' awareness of alternative arguments and, ultimately, their ability to convince the school administrators to unblock previously-blocked sites. These results suggest that the design of social networking sites associated with fostering civic engagement needs to foster use of collaborative argument and adoption of competing perspectives on an issue. (Contains 1 figure.)