This is a fun and easy game that requires a little bit of preparation. First, take a marker and draw addition problems on several index cards, using only numbers 1 to 20. Don't put the answer on the card, just the problem. For example, "5+7." Next, divide the stack of cards evenly between the two players. One player counts to three and then both players turn one card over. Each player states the answer to the problem on his card. The player who has the highest number as an answer wins and gets to take both of the cards and put them into his deck. If the numbers are the same, then the players keep those cards in the middle and draw again. The winner keeps all four cards. Play continues until one player is out of cards.
Go Fish is a classic card game that can be used to teach addition. First, take several index cards and write math problems on the cards using only the numbers 1 to 20. Be careful to have only two cards that equal the same number. For example, one card might read, "8+3" and another might read "6+5" and those would be the only two that add up to 11. Shuffle the cards. Deal seven cards to each player. If the players receive any pairs, or cards that equal the same number, they should put them aside. Now, play Go Fish by going around the circle and having the players ask "Do you have any cards that equal __." If a player has a card that equals that number, he hands it to the first player, who asks again. If he doesn't, the player says "Go Fish," and the first player draws from the middle pile. Play continues until all pairs have been found. The player with the most pairs wins.
Take a standard letter size piece of paper and draw six numbers on it, in three even rows. Photocopy this paper so each player has one of her own. Turn the paper over so the players cannot see the numbers. Using a timer, begin timing the players as you say "Go!" Each player must add the three numbers appearing vertically, horizontally and diagonally. This makes for eight separate math problems. As they add, the players write their answers down. The first player to finish (and answer all eight problems correctly) wins.
This is a fun activity that takes a classic card game and puts a math twist on it. First, take several index cards and put them into stacks of two. One one card, right a math problem such as "9+5." On the other card, write the answer. In this case, "14." Continue making these cards being careful that only only one set has the same answer. For instance, "9+5" should be the only problem that adds up to 14. When you are finished, lay the cards face down on the ground in rows. Each player takes a turn turning two cards over. If he finds a match (the addition problem and its answer), he takes those cards and puts them in a pile near him. If he doesn't, he puts them face down again in the same spot, and the next player goes. The game continues until all the matches have been found. The player with the most matches wins.