The concept of the density of a material has an important role in elementary and secondary school science curricula, but it is a difficult concept to grasp. This project explores why this should be and whether there are some simpler, more accessible notions which can serve as the basis for building a concept of density in students' minds during the later elementary school years. The study explores the effectiveness of using computer models to help students build an understanding of density. This teaching strategy proved to be moderately successful with sixth graders. It was found that the majority of students did correctly assimilate this model in a way that supported their understanding of density as an intensive quantity and that they were able to articulate some relevant differences between weight and density. It was found that this distinction was necessary for children to have success at ordering by relative densities and in understanding a phenomenon such as sinking and floating. Appendices supply a description of the computer programs, worksheets, lesson plans, and interview instruments. (CW)