This study investigated whether elementary students could collectively advance a knowledge-building discourse through judgments of promisingness and epistemic reflection. Supported by the Promising Idea Tool and its accompanying pedagogical design, 32 grade six students were involved in judging the promisingness of their community ideas, refining ideas iteratively, and explicitly reflecting on their knowledge-building discourse using knowledge-building principles. We analyzed students' online discourse using multivariate methods, including socio-semantic network analysis and content analysis. Socio-semantic network analysis indicated that the students progressively advanced their community ideas and the community became more connected over time. Content-analysis results indicated that sixth graders could collectively improve their discourse by contributing diverse ideas, negotiating a fit, and generating questions, using problem-centered uptake moves and synthesis notes. The study's findings have important implications for the design of technology-rich environments, and shed light on how teachers can use them to help learners engage in productive collaborative inquiries. [For the complete proceedings, see ED601080.]