Density is a derived quantity that can be confusing for middle school students. In this article, the author describes how he used a graphical depiction of mass and volume to guide his sixth-grade students in understanding and applying this concept. In the activity, students collected various materials, then discussed and tested whether each of the objects floated or sank in tap water. They also measured the volume and mass of each object. Graphing the data allowed them to make the important conceptual leap from their initial thoughts and findings to exact criteria for floating. It also led to a clear understanding of density through a practical application. By initiating and conducting hands-on inquiry, students were able to gain a more powerful understanding of the content presented.