What Are You Doing?
Two players stand in the center of the performing area. They both start to mime, independently from each other, any random activity. Player A asks Player B, "What are you doing?" Player B now answers the question with any activity, except the one that Player B is actually doing. At this point, Player A must mime the activity that Player B says. Once Player A is able to establish this new activity, Player B then asks the question: "What are you doing?" and then must do whatever the answer is from Player A. This goes back and forth until they break the action. The key is that both players must never stop miming, especially when they are answering the question.
In The Classroom:
This game requires a great deal of mental flexibility. To be able to mime one activity and then say that they are doing something else is surprisingly hard, especially while the player is trying to keep track of who's turn it is.
It also pushes many students out of their comfort zone, as they are required to instantly mime what the OTHER player comes up with. Watching a player just decide to go with it is great fun to watch and makes the game very entertaining.
When students first try this game, many need to be walked through it from the side. It is okay to remind them who's turn it is to ask the question.
It is very important to strictly enforce the "always miming" rule. Kids tend to stop miming in order to think, the point is to do one thing and think another. Build that Mental Agility!
Remind them that their job is to make the other player look good! NOT to trip them up or embarrass them! Giving a unique or challenging mime to perform is fine, but children (or adults) of a certain age like to say "I'm going to the bathroom" or "I'm taking a shower" or some other uncomfortable idea. (Professional improvisors will tell you that people who are trying to be clever or unique will come up with the same three or four ideas.) If this happens near the end of their time I will cut in with an "Okay, next group!" or if it happens in the beginning I will, in a sort of board voice, say, "Lets keep our clothes on, please. Come up with something else." (Some professional improvisors will also be appalled that I would think of censoring artists in this way, but those improvisors have never been a teacher in a middle school classroom. The notion that you must allow scenes that make you uncomfortable is probably the number one reason that teachers do not use improv in class. I am all for a wide window of acceptable behavior, but not an infinite one! And every professional improv troop who has done "family friendly" shows or shows for schools and have needed to tone down their language and content, this is no different.)
Team work and mental agility are the keys to this game. It is a great game for that filler time. It is also a great way to get kids more comfortable being on stage.
There isn't a lot of direct connections to common core topics with this one, it is all about developing skill and bringing a group together.
There are ten or twelve games that can be considered true "classics" that are impossible to attribute because they are everywhere, and everyone who has taken even the most basic improv classes are familiar with. This is one of them.