This is a game called Heads and Tails. I can't remember who I got it from but thank you whoever you are! It’s a nice kinaesthetic activity and is a good one for KS3 (or below). You give them sentences and they have to decide whether they are true or false. If they think the sentence is true they put their hands on their heads. If they think the sentence is false they put their hands on their bums (or hips if you prefer).
You could also show them a word and an image. If they think the word and image match, they put their hands on their heads, and if not, they put their hands on their bums.
Let me know if you can think of any other variations of this or any similar activities.