In this study, it was aimed to examine the argumentation structures of 5th-grade middle school students, while they were structuring geometric concepts in argumentation-based activities of geometric shapes. To this end, 7 fifth-grade students studying in a public middle school were included in the study. In the study, five geometry tasks involving activities based on materials of geometric shapes were carried out. The geometry tasks were structured based on argumentation, and the argumentation structures of students in the processes of structuring geometric concepts were analyzed. In the study, the argumentation structures of source-structure, spiral-structure, and reservoir-structure emerged from the student discussions and communications. According to these results, teaching activities structured based on geometric shapes and materials were observed to be effective in revealing students' different argumentation structures.