Emerging research suggests that problem solvers employ distinctive gestures as they strive to explain scientific phenomena. Because the learning sciences increasingly assign explanation a central role in science learning (Chi, Bassok, Lewis, Reimann, & Glaser, 1989; Linn & Songer, 1993; Morrison, Newman, Crowder, & Théberge, 1993), distinguishing descriptions from explanations on the basis of associated gestures could prove a useful research and teaching tool. Extending the work of McNeill (1992) and others, this article outlines a way of coding gestures that allows observers to distinguish explanation discourse from other forms of science talk. Sixth-grade science learners gesture differently depending on their discourse mode. When explaining in-the-moment, students gesture in ways that help them to predict, revise, and coordinate elements in a model. In contrast, when they describe a memorized or previously thought-out model, students time their gestures to redundantly emphasize speech. Gesture perspective, or where the speaker stands in relation to the discourse, also distinguishes descriptive transmission of knowledge from self-explanations. Whereas a describer maintains distance between himself or herself and his or her gestures, the in-the-moment explainer steps into the gesture space, assuming an inside observer perspective. In conclusion, gesture assists in the construction as well as the communication of scientific insights.