Model combining two right-triangles into a square and splitting a rectangle into two triangles. Introduce the right angle as a "square corner" and compare other angles as smaller (acute) or larger (obtuse) than it, using Ollie's Looking Glass to inspect leaf corners.
Together 1. What shapes can we make by combining two squares? By splitting a square diagonally?
Together 2. Use the corner tester: is this angle smaller or larger than a right angle?
Students complete "Looking Closely: Shapes & Angles".