We have described four levels for students' accounts of carbon transforming processes:
Level 1. Macro Force-dynamic Reasoning. Level 1 reasoning relies on macro force dynamic causal reasoning. Events are understood in terms of the actors and their enablers. The actors have natural tendencies and abilities to do certain things if they have a set of enablers. The interaction between the actor and its enablers is a macro type interaction like a push-and-pull. This type of macro interaction does not involve any hidden processes.
Level 2. Macro Events Driven by Hidden Processes. In level 2 reasoning, macroscopic changes are caused by some hidden processes. Some examples of the hidden processes are: materials changing without reaction; materials changing from or into energy; materials disappearing or being created. An initial understanding of matter and energy emerges in level 2 reasoning, in which: gaseous materials are usually not identified, materials do not have chemical identity, and energy is understood in its colloquial meaning – energy is the power to make things happen.
Level 3. Unsuccessful Constraints on Processes. Level 3 reasoning is closer to scientific model-based reasoning. First, macroscopic changes are treated as being caused by changes involving molecules. However, the notion of chemical change as atom rearrangement is still missing. Thus, students’ explanations may not identify all reactants and products correctly. Second, level 3 reasoning shows commitment to conservation principles. However, students usually cannot successfully trace matter and energy through most processes.
Level 4. Successful Constraints on Carbon Cycling. Level 4 causal reasoning emphasizes using an atomic-molecular framework—key carbon cycling processes (i.e., photosynthesis, cellular respiration, digestion & biosynthesis) constrained by three principles (i.e., matter conservation, energy conservation, and energy degradation)—to explain macroscopic events.
Mohan, L., Chen, J., and Anderson, C. W. (in press, 2009). Developing a multi-year learning progression for carbon cycling in socio-ecological systems. Journal of Research in Science Teaching.
The products of our work include a coordinated set of written assessment items, clinical interviews, teaching materials, and a learning progression framework that will be usable for teaching carbon cycling; topics in upper elementary, middle school, high school and undergraduate classroom settings.