Each student takes one card. (If you have less than 21 students, a few students can take more than one card!) Player One reads, "I have 0, who has 1?" Player two reads, "I have 1, who has 2?" Continue play until the last card, "I have 20, who has 0?" is read. Mix the cards up so that two players that read back to back are never beside each other. Add a timer so that your players can get faster and faster. While this game reinforces number recognition it is also encourages your students to pay attention while building team-work!