RUME 25
2023
Omaha, Nebraska
Magnitude Bars and Covariational Reasoning
Page: 752
In this report, I examine the recommendations made by researchers to use magnitude bars (or dynagraphs) with students to support their reasoning about quantities. More specifically, I look at implications of an undergraduate pre-service secondary mathematics teacher’s reasoning when using tasks with magnitude bars designed to support students’ meanings for geometric formulas in dynamic contexts. I illustrate the ways in which a student reasoned, ways that both resonated with researchers’ recommendations but also introduced unanticipated difficulties that resulted from the introduction of the magnitude bars. Specifically, I show two different ways of comparing magnitudes a student illustrated in the Painter Problem-using amounts of change reasoning and length comparison reasoning. The results of this study contribute to the literature on using magnitude bars to support students’ reasoning by illustrating the different ways in which a student can reason with magnitudes.