This study investigated the variation of meaning that may be assigned by students to instructional symbol systems. Toward this end, student interpretations of symbols employed to represent free fall in Boxer, a computational environment designed for innovative instructional activities in math and science, were analyzed. Four classes of sixth-graders drew pencil and paper pictures of a ball in free fall three times during a four-week unit about motion. Between picture-drawing activities, students programmed simulations of motion in Boxer. Their programs were constrained according to the Boxer simulation syntax, and both dynamic and static forms of feedback reinforced this syntax. As students repeatedly drew episodes of free fall, many adopted the symbol system utilized by the Boxer environment. However, rather than uniformly copying the Boxer syntax to their pictures, students employed the observed symbols in a surprising variety of ways. Data from the pictures and student interviews suggest that the adoption of Boxer symbols was mediated by a variety of student representational ideas. Building upon the results of other studies that address interpretation of static representations, this study suggests that uniform student interpretation of computer-based dynamic representations is by no means assured. (Contains 16 references.) (Author/MES)