Learning goals: Teacher Facing Describe (orally and in writing) ways in which two identical triangles can be composed, i.e., into a parallelogram or into a rectangle. Show how any parallelogram can be decomposed into two identical triangles by drawing a diagonal, and generalize (in writing) that this property applies to all parallelograms, but not all quadrilaterals. Full lesson plan (warm-up, activities, synthesis, cool-down prompt) from 6.1 Area and Surface Area, Grade 6.