*Higher or Lower*
A great and easy game that involves math, and works best with late primary and junior grade levels. Tell the class you are going to think of a number between 1 and 100, and their job is the figure out what that number is. They take turns guessing numbers, and you tell them whether your number is higher or lower than the number they guess. You keep going until they have figured out the number. Tell them the goal is to see if they can get the number in under 6 (or pick an appropriate number) of guesses. If using a classroom management strategy that involves points, you can also use this opportunity to give them points if they can figure out the number in under a certain amount of guessing.
You can also allow yes or no questions.
For example:
"is it an even number?"
"is it a multiple of 5?"
"is it #45?"
and so on....