In studies of analogical transfer, subjects sometimes fail to recognize that problems are structurally isomorphic because of differences in the problems' content. One potential explanation for this finding is that differences in content lead subjects to infer that the problems have different structures. This interpretation would be supported by evidence that subjects construct differing mental models for structurally isomorphic problems. In this study, we show that subjects' gestures reveal their mental models of problems that involve discrete and continuous change. Four subjects talked out loud as they solved a set of four problems that involved constant change. All subjects produced gestures as they spoke, and their gestures revealed both continuous and discrete mental models of the manner of constant change. O n problems constructed to evoke mental models of continuous change, subjects tended to produce gestures that incorporated smooth, continuous motions. O n problems constructed to evoke mental models of discrete, incremental change, subjects tended to produce gestures that incorporated repeated, sequential, discrete motions. Subjects' gestures sometimes provided more explicit cues to their mental models than did their speech. The results indicate that subjects sometimes constructed differing mental models for structurally analogous problems.