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The chapter discusses a lesson plan designed to promote students' thinking and dialogue about geometric shapes. The lesson, titled "Describing Shapes", involves pairs of students taking turns as describer and drawer, with the goal of drawing a two-dimensional compound shape based on verbal instructions. The activity has three stages: Stage 1, where the describer talks but the drawer does not; Stage 2, where both can talk; and Stage 3, a whole-class discussion to summarize key points.The chapter also provides suggestions for lesson study focus, including:* How students describe their shapes* What changes when both students can speak* How students discuss ideas about dialogueAdditionally, the appendix provides resources such as a lesson plan, possible shapes for the task, and an observer's sheet to record observations during the activity.