This game for two players provides students with practice in whole number addition and subtraction while developing strategic thinking. It is played on paper on a 0-20 number line. Player 1 crosses off two numbers and circles either their sum or difference. In each successive turn players cross off the last circled number and one of their choice, and then circle the sum or difference. The player who makes the last possible move wins. The game also may be played co-operatively. The Teachers' Notes page offers suggestions for introducing the game, discussion questions, and extension ideas.