Draw a chalk grid on a driveway or patio. The grid should have at least 25 squares –five down and five across– with each square being about a foot across. You can use a yardstick or measuring tape in order to make the squares more exact.
Write one number in each square of the grid. The numbers can be as high as you would like, based on the level of subtraction that children playing the game have mastered. For example, a child who is just starting to learn subtraction should have only one-digit numbers in the grid. A child who has become proficient in subtracting three-digit numbers from each other can have very large numbers in the grid. Make sure that there are no clusters of all large or all small numbers anywhere in the grid.
Make a chalk line about six feet away from the grid. (You can make the line closer or farther, depending on how well the children can throw.)
Give each child two bean bags.
Instruct children to throw their bean bags on the grid and take note of the numbers they fall on. Children should then subtract the smaller number from the larger number to get their final score for the round.
Play four more rounds, adding to their previous score at the end of each round. The child with the highest score at the end of five rounds wins the game!