What is the role of gesture in classroom science talk? This study first approaches the question generally, by asking how children communicate their knowledge of the seasons (through language, gesture and/or deictic references to props). We then ask how gestures function as they interplay with language in students' science talk. A typology, coded for High or Low lexical and gestural specification, summarized how thirteen sixth graders externalized their knowledge of seasonal change. Applying it to sixteen student discourse excerpts, we tested its usefulness as an analytical tool. Representational gestures functioned as redundant to, or enhancing of ideas expressed through speech, or alternatively as carriers of scientific meaning. Findings show that gestures are an expected mode of communication in the science classroom. They can reveal student knowledge that is missing from verbal communication. Additionally, gestures may figure crucially in the construction as well as the communication of scientific insights.