Materials needed: Piece of cardboard, ball, water container
We don't have a dunk tank for the 5th graders this year, so you'll have to find somebody to be the dunk tank! This activity needs three people: one to throw, one to be the dunk tank, and one to get dunked (or really, splashed).
Take a large piece of cardboard and draw a target on it, and get a ball to throw at the target. Then, get a cup or pitcher and fill it with water. The "dunk tank" person holds the target out with one arm, and the water container in the other hand, over the person getting dunked who is sitting on the ground. The thrower steps back and throws the ball at the target.
If the ball misses the target, nothing happens. But if the ball hits the cardboard target, the "dunk tank" dumps the container of water over the sitting person's head! They just got "dunked".