The 4th Grade Performance Expectations (PEs) are organized into five different bundles of PEs in this model, using a topical arrangement. Bundle 1 focuses on organism structure and function and information processing. In Bundle 2, the abstract concept of energy transfer is introduced alongside a focus on information transfer. Bundle 3 extends the study of energy to include cause and effect relationships between energy and collisions. In Bundle 4, students are introduced to waves and their properties. The idea that waves can cause objects to move can be used to facilitate student understanding of the scale of the rate of weathering or erosion in certain environments. Bundle 5 builds on the third grade focus on force to facilitate students’ understanding of Earth systems and their processes of change.