Resumen

This study investigates secondary students’ understanding of isometry (symmetry, rotation and translations) using dynamic geometry environment with touchscreen (DGEwT). The research question addresses issues concerning geometrical reasoning of Brazilian learners without previous knowledge regarding isometry. Data came from videotapes, written notes for each proposed task and on the icon sheet, and from screen recording. The analytical process was mainly based on the geometrical reasoning and related procedures. One designed task is shown and analyzed. Applying reflectional symmetry ideas, using procedures based on straight line and performing simultaneous touches on the screen, students achieved the composition of rotation and translation movement naturally and synchronically. The study highlighted the relevance of isometry in both school and teacher training curriculum.