Density is the first intensive physical quantity students encounter that can be understood in terms of an underlying model, the particulate theory of matter. Learning about density provides students with explanations for a range of phenomena such as sinking and floating, and changes of state. Teachers report, however, that density is a difficult concept for students to grasp. Researchers conducted pilot studies to determine whether students can understand a visual analog of density presented in computer graphics more easily than they can understand the concept of density inferred from manipulation of real world materials. Second-, fourth-, and sixth-grade students received two sets of parallel tasks: one involved manipulation or real materials and the other involved shapes presented in a computer display. Findings indicate that experience with computer models can help students to think about the difference between steel and aluminum cylinders as an intensive one--that is, stemming from the kind, not the amount of the material. Younger children, however, need help to see the computer analog as a "model" of density. (CW)