Throw away (or eat) the cakes from two circular cake boards. (Try to get boards that are different colours on each side.) Clean (by licking or sponging) the boards. Make a straight cut in each board from centre to circumference. Now slide the cuts together so that the boards overlap each other with the different colours showing.
For a starter ask pupils what type of angle they can see - you can specify which angle if you want. This allows you to change the angle quickly. Remember you can keep the angles as they are and turn the whole board round. This helps pupils appreciate that an angle does not have to have one of its legs vertical or horizontal and can be orientated in different positions. By moving the circles on top of each other you can change the angle and pupils can see that angle is a measure of turn.
Ask pupils to estimate the size of the angle shown. If you want to measure for yourself you can hide a protractor behind the boards (or mark one on the boards) and secretly read it. Repeat this so they make five estimates. Read out the answers so they can mark it themselves with, say, two marks if they are within 10 degrees, one mark if within 15. Repeat with another five estimates and let them see if they improve.
Peter Ransom is leading mathematics teacher at The Mountbatten School and Language College, Romsey, Hampshire