Introduce the activity by discussing any previous knowledge or experience the students may have with subtraction. Talk about how, why, and when people use subtraction outside of school. Allow the students to contribute ideas and write down their ideas on chart paper or a chalkboard.
Explain to the students that they will be playing a subtraction game. Tell them they will be working with a partner and taking turns hiding unifix cubes and guessing how many are hidden.
Pair the students up and tell them to find a good working space in the room. Pass out one bin of unifix cubes to each partnership. Ask a volunteer to distribute one piece of construction paper to each partnership. Ask another volunteer to pass out lined paper and pencils to each student. Demonstrate how to fold the paper in half and stand it upright like a triangle on the floor or desk.
Ask the partnerships to choose a certain number of cubes from the bin and stick to that total for the first few rounds. Remind Partner A to close his or her eyes while Partner B hides some of the cubes under the paper. Tell the partner B to reveal the hidden cubes after partner A guesses. Instruct students to take turns hiding and guessing.
Tell students to keep track of their subtraction facts on the lined paper. For instance, if the partnership starts out with 34 unifix cubes, and during the first round Partner A hides 12, Partner B should guess and then write 34 - 12 = 22 after figuring out the correct answer.