As the cases in this chapter suggest, it takes considerable time and effort to introduce students to ideas about atomic-molecular theory in a meaningful manner. It is important to take that time at the middle school level for several reasons.
First, understanding atomic-molecular theory opens up many productive new avenues for investigating matter. For example, it introduces the concept of chemical change, which research suggests is not really accessible to students with only macroscopic criteria for identifying substances.
Understanding atomic-molecular theory also helps students more clearly understand what substances stay the same and what substances change during the water cycle. In addition, many important topics across the sciences—osmosis and diffusion, photosynthesis, digestion, decay, ecological matter cycling, the water cycle, the rock cycle—depend on an understanding of atomic-molecular theory.
Finally, atomic-molecular theory gives students an opportunity to begin developing an understanding of and respect for the intellectual work and experimentation needed to formulate successful scientific theories.
In current practice, atomic-molecular theory is often presented to students without careful attention to how their ideas develop through instruction or how to help them link science with their emergent ideas and relevant everyday experiences. As a result, as research makes clear, the majority of students fail to internalize the core assumptions of atomic-molecular theory, and they are unable to understand such important ideas as chemical change. Perhaps more importantly, students are not given the opportunity to recognize the standards that a scientific theory is built on, how it is formed, and why it cannot be challenged by other theories that do not meet the same rigorous epistemological standards. Without an understanding of those epistemological standards, students will not know the grounds on which they should test and believe scientific arguments.
Learning progressions are a promising way to design and organize science learning. Recognizing this, teams of educators and researchers are actively developing learning progressions with support from the National Science Foundation and other sponsors. For now, fully developed, well-tested learning progressions that are ready for broad application will have to wait. But that does not mean