<p>Collaborative knowledge building (CKB) encourages students to build on knowledge at the group level through peer interactions. Process and summative assessments are essential methods for understanding and promoting the quality of CKB, but few studies focus on the assessment at the group level. To provide an operationalizable measurement of CKB process, this research conducted a process and summative assessment of Knowledge Forum data from groups of graduated students, then conducted group classification based on the assessments, and further examined the transitional and developmental characteristics. The research proposes an operationalizable measurement equation for assessing the quality of the CKB at the group level, it also proposes a summative assessment based on the final knowledge artefacts produced by the groups. Group classification was identified based on the results of both the process assessment and the summative assessment. Using the process mining method, this research visualized and demonstrated the procedural details of learning engagement within different group classifications during the CKB processes. The research identified four distinct group classifications based on the process assessment of CKB and the summative assessment of final research proposals. The results of process mining showed that four group classifications exhibited varying transitional and developmental processes in terms of social, cognitive, and metacognitive engagement. Results showed that the high-quality CKB process and performance primarily depended on progressive interactions based on group-level knowledge negotiation or perspective exchange, rather than merely interacting on questioning or information sharing. Three significant pedagogical implications and three assessment implications were proposed.</p>