This study explores how elementary teachers and students use hedges (tentative words such as "maybe") and boosters (expressions of certainty such as "clearly" and "obviously") during science inquiry discussions. Drawing upon semiotic theory, we examine explicit thematic patterns (semantic meaning relations among science concepts) as well as hidden social, nature of science (NOS), and epistemological meanings co-constructed and communicated by teachers and students. It was found that a kindergarten teacher's discussion was mostly unhedged and boosted ("absolutely"), with the use of hedges ("may," "might," "could") limited to an unexpected encounter with an undeveloped egg toward the end of the lesson. In contrast, a fourth-grade teacher's discussion was predominantly hedged, with the use of boosters limited to isolated episodes concerning the nature of scientific inquiry and experimental variables. Unhedged and boosted communication led to the co-construction of an unproblematic or factual body of scientific knowledge (transitivity, circumstantial, and nominal meanings), whereas hedged communication produced a problematic or tentative body of scientific knowledge (logical and taxonomic meanings). It is emphasized that unproblematic knowledge communication may be paralleled by NOS miscommunication. We argue that teachers should be provided with professional development that can increase their awareness of the risk of NOS miscommunication.