Elementary students' argumentative and explanatory mathematical writing about fractions

Mathematical writing (MW) is an important yet underutilized form of mathematics discourse. Given the lack of attention to MW, there are few resources to support the implementation and assessment of MW. This study responds to the lack of resources by describing a MW unit focused on fractions that was implemented during a summer school program to support rising fourth grade students with explanatory and argumentative writing. Findings from the study revealed that students used different forms of reasoning about fractions to compose their mathematical argument and explanation. We also identified five categories that captured how students communicated a mathematical argument and explanation: writing organization, precise mathematical vocabulary, mathematics content, mathematical representation, and characteristics specific to a mathematical argument/explanation. The five categories led to the development of an analytic rubric for argumentative and explanatory writing.