When I was in 5th grade, the kids in my neighbordhood and I invented a great game. The game mechanics are a bit lengthy to describe here, but they involved two teams, each taking turns to question the other team on an imaginary object. The team with the most consistent answers won. We played this game for months, and enjoyed it a great deal. As time went on, we got better and better at it, making it very challenging to trip the other team up with difficult questions, and thus making the game very exciting and intellectually stimulating.