On the board are three shapes, each with its name beside it: a rectangle, a right-angled triangle, and a wide arrowhead. Look only at their corners.

Now hold that square corner in your mind and look again. One shape has a corner that opens out further than a square corner does. Which shape is it, and which corner do you mean?

We will test the corners of real paper shapes with a folded-paper corner that makes an exact square corner. Every time we push it into a corner, ask one question: does it fit exactly, or is the corner smaller, or wider? Watch the fit at each corner and be ready to say acute, right or obtuse.

Now we test corners together. Each of you has your own paper shapes and a folded paper corner.

We will work through the same five shapes:

• the square
• the right-angled triangle
• the rectangle
• the arrowhead
• the equilateral triangle

Say what you expect each corner to be before you test it.

Testing round. Use the folded paper corner on your shape cards to find:

• a shape with every corner a right angle
• a shape with exactly one right angle
• a shape with a corner wider than a right angle
• how many right angles a rectangle has — check every one