In previous units and lessons, students compared the lengths and weights of objects. Students learned that three-dimensional shapes are solid. In this lesson, students learn about an attribute of solid shapes: capacity. Initially students compare two containers where it is visually obvious which one holds more. After this initial discussion, the cups or containers that students are comparing should have capacities that are not obviously different. For example, a shorter, wider cup and a taller, thinner cup.

Although this lesson requires new materials and preparation, it is extremely helpful for students to have the experience of working with liquids in different shaped containers to build a conceptual understanding of comparing capacities.