KS34: We can be fooled in the way we perceive objects and exercises, and using optical illusions show how this happens. Junior texts, such as Spotlight Science (Nelson Thornes, pound;8.77) have simple, photocopiable illusions. Optical Illusions by Bruno Ernst (Taschen, out of print, but available through libraries), has more complex illusions, including photos of a concave face by Sandro Del-Prete, which the brain interprets as convex. Ask Jeeves for Kids (www.ajkids.com) contains explanations of how some illusions work.
Memory games are also useful, especially those that can be used to demonstrate successful learning and revision techniques. Try You and Your Mind: Students' Book (Longman, out of print, but available through libraries) for some simple examples.