Reasoning, Granularity, and Comparisons: A Unit-Based Method for Characterizing Students’ Arguments on Chemistry Assessments

In a world facing complex global challenges, citizens around the world need to be able to engage in argumentation supported by scientific evidence and reasoning. In order for coming generations to have proficiency in this skill, students must be provided opportunities to develop and demonstrate argumentation science classrooms, including on assessments. For example, students can be provided with assessment items that explicitly ask them to reason from evidence. Alongside these assessment items, researchers and educators need methods to evaluate students’ written arguments. In this study, we present a unit-based method for characterising students’ arguments on chemistry assessments. This unit-based method identifies units (links, concepts, comparisons) within one’s argument, and uses these units to evaluate an argument based on three dimensions: reasoning, granularity, and comparisons. To demonstrate this method, we report our findings from using it evaluate two different organic chemistry questions: (1) justifying why one of three bases would drive an equilibrium towards products (N = 170), and (2) justifying why one of two reaction mechanisms is more plausible (N = 122). Lastly, to translate the method into a rubric for educators, we compare a scoring system based on the unit-based method against a traditional scoring system. As well, we report our findings from interviews with educators (N = 4) to invite their feedback on the rubric and its dimensions.