Lower secondary students' reasoning competency in a digital environment: the case of instrumented justification

Our work stems from the need to deepen digital technology aspects of KOM’s competencies descriptions. Specifically, this chapter contributes to partially bridging this research gap by offering a tool to analyze how a digital interactive environment like GeoGebra can contribute to lower secondary school students’ reasoning competency in a mathematical domain at the crossroads between algebra and geometry. First, we present an analytical tool that makes use of Toulmin’s argumentation model together with the scheme-technique duality from the Theory of Instrumental Genesis. We then use the tool to analyze excerpts from two students’ efforts to solve a task in GeoGebra where objects are represented algebraically and graphically. The analyses show the analytical tool’s potential, supporting the introduction of the notion “instrumented justification” to frame the process captured by such a tool.