This study investigated synchronous discourses involving student collaboration in fixed groups during an introductory research methods course's first 8-week phase, and opportunistic collaboration during its second 8-week phase. Twenty-seven Chinese undergraduates participated in online discourse on Knowledge Forum as part of the course. A multi-faceted analysis was performed to examine different aspects of collaboration-interaction patterns, knowledge characteristics distributed over inquiry, discourse patterns, and knowledge advances that emerged from discourse threads. The results show little variation in social interactions, but substantial differences in knowledge distribution between fixed groups. Groups that were productive in constructive discourse tended to generate higher-level questions and ideas. When engaged in opportunistic collaboration, the students were capable of engaging in a large range of interactions and of contributing higher-level questions and ideas; however, they were constrained by making little use of metacognition and having scattered interactions. Additionally, this study tested the relationship between online discourse and individual performance in the end-of-course assessment tasks. The results indicate that actively participating and contributing high-level ideas were positively correlated with students' domain knowledge. The study's implications for understanding online discourse dynamics within and across fixed groups and opportunistic collaboration in a computer-supported collaborative learning (CSCL) environment are discussed.