What are things made of, and how can we explain their properties?
What changes, and what remains the same, when things are transformed?
How do we know?
A well-designed learning progression on atomic-molecular theory won’t mention atoms and molecules in the earliest grades. The notion of atoms, chemical substances, and chemical change are complex ideas that take time to develop, test, expand, and revise. These ideas are too advanced for most young children, although some may have heard about atoms and molecules and may use these terms or ask questions about them. The point is to emphasize the goal of understanding concepts, which is very different than merely memorizing vocabulary or definitions. By not emphasizing technical terms in the early grades, the teacher avoids sending the counterproductive message to students that science is about memorizing terms and definitions for phenomena that they fundamentally don’t understand.
Even in the later years of elementary school, students may not be ready for the idea that all matter is composed of atoms and molecules. They first need to develop a sound macroscopic understanding of matter. In general, one of the most difficult transitions children must make during the K-8 years is linking macro-level processes with micro-level phenomena. For example, elementary school students may think that, at a molecular level, wood will look like tiny pieces of wood, rather than consisting of molecules. It takes several years for students to work out the subtleties of understanding the basic constituents of matter (atoms and molecules) and how they combine to create larger units.
It is important to keep in mind that a learning progression is not a lockstep sequence. Different classrooms, and even different students within the same classroom, can follow different pathways in coming to understand core science concepts. There are many ways to learn that all matter is composed of atoms and molecules.
The following case study involves a classroom of kindergartners who are investigating the idea that different objects are made out of different materials, that there is a difference between what an object is used for (its function) and what it is made of (its material kind), and that these different materials have properties that can be discussed, examined, and described.