How to Play:
The teacher calls out a number (e.g. four), and the students have 10 seconds to get themselves into groups of that size.
It might be impossible for everyone to get in a group every time, but each new number gives everyone another chance.
In the beginning, just call out single numbers. Once students get the idea, you can call out addition or subtraction problems (e.g. 7-4 = groups of 3).