Here is a trick that will mystify your students and give you plenty of opportunity to explore the physics of mirrors.
Take a cardboard box and replace one side with a sheet of plastic, such as an overhead transparency. Cover the inside of the box with plain wrapping paper. Take a mirror and place it diagonally into the box, so that the reflecting surface of the mirror is angled towards the plastic side. The top of the mirror should meet the top of the plastic.
To make the illusion more appealing you could stick half a plastic ball on to the centre of the mirror. When you look through the plastic window you should see a suspended ball. The box should look complete, as the sides are reflected in the mirror.
Now cover the top and the outside of the box so you can't see how you're creating the illusion. Make a hole in the middle of the box's top back edge.
Place your box on a table, and seat the children on the floor around it.
Tell them that you have managed to suspend a ball in a box with no visible thread!
Then say that you can make things disappear. Take a postcard - or a can if your box is large enough - then say the magic words and place the object into the hole in the top of the box. It disappears!
You can make these boxes from an A4 piece of card. Use mirrored card to make the angled mirror. You can create symmetrical patterns on the inside of the box and see what they look like when you add the mirror.
Sophie Duncan is project manager for science at the BBC www.bbc.co.ukscience