Box Diagrams to Assess Students' Systems Thinking about the Rock, Water and Carbon Cycles

Abstract

Box-diagrams of reservoirs and processes that describe the rock, water and carbon cycles were used in a general education course as instructional and assessment tools. Students overall success at constructing correct box-diagram models of the water cycle demonstrates that they have three critical abilities: 1) to identify substances, locations of substances and processes that move and change substances in a system, 2) to organize the substances and processes within different frameworks and 3) to understand the generally cyclic nature of a system. Many students lack a fourth critical ability, to recognize parts of a system that are not readily apparent or visible. Students who lack this fourth ability are not able to construct diagrams with appropriate ions, molecules and/or chemical reactions. This lack of appropriate mental models is the major source of error in students' attempts to describe movement and change of matter with rock and carbon cycle box diagrams. Students have greater success with box-diagram models of the water cycle because chemical reactions were not included in the water cycle. Phase change is important in understanding the water cycle and students show evidence of poor understanding of condensation.