This research examined discourses in classroom and online learning environments where the Knowledge Building Community model was enacted to foster deep understanding in science learning in Singapore primary classes. This study posited that discourse is a fundamental form of learning that reveals how knowledge building is enacted and embodied by a community of learners. Discourses in classroom lessons and online postings were analyzed from both quantitative and qualitative views. Overall, the discourse analysis of the verbal activities in classroom lessons showed clear signs of IRE (Initiation–Response–Evaluation) patterns of discourse, while more diversity of ideas and questions were found in Knowledge Forum postings. However, online discourse showed some instances of incorrect group thinking and fear of appearing ignorant. In conclusion, we discuss implications of findings and future research directions for creating pervasive knowledge building discourse.