This is a fun combination of the game Battleship, Rock/Paper/Scissors, and Math Problems.
1.) Put a grid on the board 1-5 on the bottom and a-z along the side. (Adjust as you wish)
2.) On a piece of paper draw the same grid and secretly place battleships on your paper.
3.) Split the class into two teams, have one from each team go to the board and play rock, scissors, paper and the winner gets to answer a math problem.
4.) If correct they get to put on X on the board and you let them know if he hit your battleship.
5.) If they answer math problem wrong, the other child gets to try to answer and then put an X on the board.
I have used this with Elementary and Middle, though it can work with any age as long as the math problem is level appropriate. Also, I have eliminated rock/paper/scissor for the younger kids if many do not know how to play.