This research explores the ability of grade 2 students to engage in productive discussion about the state of their knowledge building using group-level feedback tools to support their metadiscourse. Two aspects of knowledge work were common to the comparison and experimental classes: "Knowledge Building talk" (KB talk) involving teacher-student discussions and the use of Knowledge Forum, an online environment optimized to support Knowledge Building/knowledge creation and to represent and support student work and KB talks. Students in experimental conditions additionally reviewed visualizations of vocabulary use and discourse patterns during KB talk time. Two formative feedback visualization tools were co-developed by the classroom teacher and researchers to show (a) overlaps and discrepancies between words students used in their Knowledge Forum notes and words used by writers more knowledgeable in the field and (b) frequency of discourse moves indicated by students' use of epistemic discourse markers in Knowledge Forum.?These visualizations served as grounding for KB talk concerned with interpreting the visualizations and considering their implications. A comparison of two classes similar except for presence or absence of these visualizations showed significant effects favoring the experimental class in domain-specific vocabulary, repertoire of discourse moves, scientific understanding, epistemic complexity of ideas, and interpersonal connectedness of online discourse.