Children seem to enjoy difficult work, work which tests their abilities and provides a sense of their growing power. They exult in giving their maximum effort. For example, a tiny child will struggle to carry a tray with juice glasses or push a heavy wheelbarrow whereas school-age children, if allowed to make up their own problems will prefer to sink their teeth into a challenging equation (I + 2 + 3 + 4... + 10)2 rather than drill on 3 + 5 = ... and 6 + 2 = ... .