The lesson is structured in the following way:
• Before the lesson, students attempt an assessment task individually. You review their work, and formulate questions to help them improve their solution.
• During the lesson, students first work individually, using your questions, to improve their solutions.
• They then work collaboratively in pairs or threes on the same task. They justify and explain their decisions to peers. Working in the same small groups, they critique examples of other students’ work on the task.
• In a whole-class discussion, students explain and compare the alternative approaches they have seen and used. Finally, they again work individually to reflect on their solutions to the task.
This lesson unit is intended to help you assess how students reason about geometry and, in particular, how well they are able to:
Use facts about the angle sum and exterior angles of triangles to calculate missing angles.
Apply angle theorems to parallel lines cut by a transversal.
Interpret geometrical diagrams using mathematical properties to identify similarity of triangles.