Students become familiar with the many types of models that they use daily, as well as others that are introduced, and the usefulness of models to the scientist. Students also characterize systems and their function within models. For more information on models, see the article Grosslight, L., C. Unger, and E. Jay (1991). "Understanding models and their use in science: Conceptions of middle and high school students and experts." Journal of Research in Science Teaching. Vol. 28, No. 9, Pp. 799-822. The relevant points are summarized below.

• What is a model?
  A model is a way of describing or representing, often mathematically, an idea, a thing, or a condition so that all of its applicable properties are demonstrated/obviated.
  
• What value is there in developing models?
  Models allow the designer to target and depict specific variables for study and manipulation, which might not be possible in the natural world.
  
• What is a system?
  A system is an organized group of parts, which usually are connected in such a way that a change in one precipitates change in others.
  
• What value is there in knowing or understanding systems?
  The very complexity of the natural world can discourage children from attempting change. However, creating a model of a system allows them to experience the complexity while yet controlling chosen aspects so that they can effect change.
  
• What is involved in systemness?
  
• What is involved in kids learning about systems?
  
• What can/should teachers do to help kids understand systems?
  
• What does understanding look like? Interconnectedness, measurement samples and sampling, stems? environments? science literacy? interests, wonderings, etc.
  
• How are models developed?
  
• What function does a student-developed model serve in developing scientific literacy?
  
• How can student models lead to understanding of natural environments?
  By using the natural environment (ponds, lakes, wetlands, rivers, etc.) as a biological and ecological study area of such topics as diversity, classification, water quality, interactions and interdependence, and so on, students have a foundation on which to base their model aquatic systems. These models serve as forms for observation and experiment, the results of which can be applied back to the natural environment. Students must analyze their research question, model, and results for meaningful warrants to the natural setting. Development of a convincing argument in this setting may require changes in assumptions, experimental and observational processes and procedures, and data, data interpretation, and data representation.
  Specific objective: Students use their knowledge of natural systems to design an experimental/observational system for study and data collection. They use their results to infer and extrapolate back to the natural system.