The purpose of this game is to ensure students count in 'chunks' rather than by ones. Technically, they're learning how to subitise so that when they need to add 35 and 7, for example, they can mentally split 7 into 5 and 2, thereby arriving at 42 quickly and painlessly. Here's how the game works:
1. Remove all face cards from a deck of cards. One deck is needed for each player.
2. Sort the cards by number so that you have groups of four of each number together.
3. Combine the Ace to 4 cards, shuffle them, and place them face down to the left of the player.
4. Place the rest of the cards face up in front of the player, in a single stack with four 5s on top of four 6s, etc. up to 10s. Move the stack maybe 30 cm away from the player to allow room to play the game.
5. The number on top of the stack is the target number, in this case starting with 5s. For each round, students are allowed to turn over one fewer cards than their target number, so when making 5s, four cards are turned up, when making 6s, they may turn up five cards, etc.
6. Now the play can begin. Turning up the allowed number of cards from the left-hand pile, the player combines exactly two cards to make the target number, then places these in a new stack to the right. Those two cards are replaced by new cards from the left-hand pile, and play continues. If all goes well during the round, players never get stuck and cannot play, and the cards match perfectly at the end of the round. If players get stuck because they can't make an appropriate pair, they lose that round, shuffle the cards they were playing with, and try again. If at the end of the round players are left with cards that don't combine to make the target number, there was a 'whoopsie' somewhere, and they shuffle and try again.
7. After 5s are mastered, the four 5s are added to the A-4 group, they are shuffled together and placed upside down to the left, and the play continues with the target number of 6, which should be showing on the face-up pile in front of them.
8. I have no doubt that playing this game alone at home would not have nearly the appeal of playing it in a group setting, and it helps immensely to joke about 'whoopsies' so that starting a round over doesn't become depressing. Also, to keep momentum going it's best to only do three to four target numbers in a session, so if you start with 5s, stop at 8s maybe, and another time start with 8s and finish with 10s.
Happy playing!