A group of 8 and upwards working in pairs is best for this game. You need to prepare categories of words or phrases in advance and print them so there’s one word or phrase per A4 sheet, written as large as possible.
The most obvious category would be verbs written in different tenses (i.e.: buy, bought, have bought or drive, drove, driven) but you could also use countable and uncountable nouns, say and tell or ing – er adjectives.
You need a song which the group already knows for this game, I use The Grand Old Duke of York. You also need three boxes or rubbish bins.
Let’s imagine we’re going to use the verb idea… Each bin is placed somewhere in the room, three corners perhaps, and the group congregates in the middle with all the words face-down and mixed up together in a rough pile. Decide that one bin is the Past, one the Present and the other, the Past Participle (or present perfect, depending on how you have approached the grammar). Each pair takes a verb on a piece of paper and, immediately, the rest of the group starts to sing the song as quickly as possible. Meanwhile the pair with the verb have to make a paper ‘plane and fly it towards the appropriate bin. The idea is to fly the ‘plane into its box or bin before the others have finished the song. If you want to, you can change the song half way through the game.
Obviously, they are all focused on completing what they need to do and so the language point becomes obscured amongst the fun of making paper aeroplanes and singing.
Naturally, you could use other criteria for this, not necessarily grammar-based at all.