You need two players.
Player one chooses two cards that DO NOT equal 10. He/She does not show these cards to the other player.
Player two begins placing cards face up -- one at a time on a table/desk.
When two cards on the table make 10, he/she covers those cards with two other cards that are face up also. He/She can only cover two cards that make ten, not three. For example: 8,2. 9,1. 6,4. NOT 7, 2, 1.
The second player continues to cover cards that make ten until he/she runs out of cards.
Then, he/she begins picking up stacks of cards that make 10. For example, he/she will pick up a stack with a 4 and a stack with a 6. Then, the child will pick up a stack with a 7 and a stack with a 3. Eventually, only two stacks of cards will be left.
The second player is holding two cards. There should be two stacks left. If the cards left are a 7 and a 1, the second player should be holding a 3 and a 9. Basically, the cards will make 10. Thus, the student "guesses" the cards in the other player's hands.