Learning progressions have many other potential benefits. They can draw on research about children’s learning in determining the scope and sequence of a curriculum. They can incorporate all four strands of scientific proficiency. Since they are organized around core concepts, they engage students with meaningful questions and investigations of the natural world. They suggest the most appropriate ages for introduction of core concepts. And they can suggest the most important tools and practices to assess understanding.

In this chapter, we’ll be examining a learning progression based on the atomic-molecular theory of matter. The idea that all matter is composed of atoms and molecules is a core scientific concept that all students should master. It allows for the integration of many different scientific findings and explains otherwise puzzling aspects of the physical world. It allows for links to be made between various scientific disciplines, including physics, chemistry, biology, and geology. We explore this learning progression to illustrate the intermediate levels of understanding achieved at various points throughout the K-8 curriculum and how this understanding is rooted in science and learning research. We intend for this to serve as an example that can be further elaborated, tested, and emulated in the service of developing learning progressions in other areas of study.

The learning progression in this chapter is divided into three grade bands—grades K-2, grades 3-5, and grades 6-8⁴—with a case study at each grade band that focuses on one or more of the concepts covered as part of atomic-molecular theory. This learning progression was designed so that students can give progressively more sophisticated answers to the following questions: