When is less more? Investigating gap-filling in proofs without words activities

In activities based on proof without words (PWW), we developed, students are given a PWW– a diagram that alludes to the proof of a mathematical theorem. The students work collaboratively to construct a proof alluded by the PWW, and then each student writes and submits a proof attempt. In a 3-year design-based study, we investigate and develop PWW-based activities for advancing upper secondary students' proficiency in constructing proofs. We use the concept of gap-filling as a theoretical framework. In a nutshell, gap-filling is an action of adding information absent in a text that a reader does for sense-making. We inquire whether secondary school students independently construct a proof when a PWW is at their disposal, what characterizes those gaps that students identify and fill, and how PWW design principles influence students’ gap-filling. We identified four categories of gaps: key idea, generality, constructional, and figure property justifications. We find that students mainly fill key idea gaps but not generality gaps and that PWWs that presented the construction procedure led more students to fill the constructional gaps. However, PWWs that did not explicitly present some figures’ property led more students to fill those justification gaps. We identify five PWW design principles that can enhance secondary students’ gap-filling and conclude that a meticulous design paves the way to implement PWW-based activities for fostering mathematical proving.