Questions about the suitability of cognitively-oriented instructional approaches for students of different academic levels are frequently raised by teachers and researchers. This study examined student participation in knowledge-building discourse in two implementations of a short inquiry unit focusing on environmental problems. Participants in each implementation consisted of students taking a mainstream or an honours version of a tenth grade social studies course. We retrieved data about students' actions in Knowledge Forum[R] (e.g., the number of notes created and the percentage of notes with links), and conducted a content analysis of the discourse by each collaborative group. We suggest the findings provide cause for optimism about the use of knowledge-building discourse across academic levels: there was moderate to strong evidence of knowledge building in both classes by Implementation 2. We end with suggestions for focusing online work more directly on knowledge building. (Contains 4 tables.)