I split the class into two teams (in one class I have girls against boys but in another class I have just divided the room down the middle) and when we play the game each side decides on a volunteer to come to the front, facing the class so they can’t see the board (one team at a time).
A word is shown on the IWB and each time the word is answered correctly I display another. I normally have around 7-8 key words from the topic per team. The quickest team to get to the end of their set of key words wins.
This works really well but it is important to set some ground rules such as not using words that rhyme with the word on display. I’ve yet to come across a class who doesn’t like the concept.