While the teacher's role is generally recognized to be important in supporting knowledge building, it is an undeniable fact that most teachers do not have a deep understanding of what knowledge building is, or even the experience of engaging in knowledge building. This paper reports on a study of students' collaborative inquiry conducted on Knowledge Forum® under a situation where the teachers were generally supportive of the educational idea but did not have the exp ertise or commitment to engage in sustained facilitation of the learning process. The findings reveal that students will still occasionally be able to engage in knowledge building discourses even without teachers' facilitation. Students' ability to engage in meaningful exploration of ideas depends very importantly on whether they can locate inquiry questions that are within their zone of proximal development. This facilitation role is even more important when the students involved have relatively lower academic achievement.