This interventional case study adopted a data-supported reflective assessment (DSRA) design to help pre-service teachers (PTs) engage in effective Knowledge Building (KB) and examined the mechanisms of this design to support PTs' productive KB discourse. The participants were 80 PTs from two classes taking the same course. Statistical analysis of indices from social network theory and content analysis of the participants' Knowledge Forum discourse revealed DSRA's positive influence on PTs' KB discourse. Thematic analysis of the PTs' prompt sheets, supplemented by analysis of classroom videos and classroom observations, revealed four mechanisms by which the DSRA fostered PTs' KB: (1) identifying promising directions for further inquiry; (2) navigating data for extending collective focal ideas; (3) integrating separated keywords and identifying problems for further inquiry; (4) and improving "storylines" in the collective inquiry process and making numerical values meaningful. These findings extend the literature by revealing the mechanisms by which learners engage in productive shared regulation which are crucial for successful inquiry and KB. The findings also have significant implications for teacher educators and researchers seeking to design technology-enhanced learning to develop PTs' higher-level KB competencies.