Can't believe I haven't done this before. You have your normal noughts and crosses grid etc, but instead of just having one child from each team give an answer, everyone in the class writes the answer on a mini whiteboard. You then pick a name at random (lolly sticks are my favourite modus operandi here!), making sure it's someone from the right team and they show you and read out their answer. If they get it wrong, you pick out a name for the opposing team. Works well and its actually quite a good settler. Everyone is involved too, which means less heavy handed classroom management!