Helping students gradually develop collective knowledge is critical but generally faces great challenges. Employing a quasi-experimental design, this study investigated the impacts and mechanisms of analytics-supported reflective assessment on the collective knowledge advancement of undergraduates. The experimental group (n = 55) engaged in Knowledge Building inquiries with facilitation through analytics-supported reflective assessment, while the comparison class (n = 38) pursued Knowledge Building inquiries facilitated by portfolio-supported reflective assessment. This study found that analytics-supported reflective assessment positively and significantly influenced undergraduates' collective knowledge advancement. Path analysis revealed the mechanisms of analytics-supported reflective assessment for supporting undergraduates' collective knowledge advancement--the undergraduates' metacognitive engagement and cognitive engagement influenced each other, further influencing their contribution to collective knowledge advancement and domain understanding. This study holds significant practical implications for fostering students' knowledge building, inquiry, and metacognition by designing technology-enhanced learning environments as collaborative and metacognitive tools. Additionally, the study offers insights into the processes and mechanisms of reflective assessment, contributing to an understanding of how it enhances students' development of higher-order skills.