Divide into two teams. (Boys against girls usually works, provided the numbers are equal, or at least close enough.) Take turns asking questions to each team. If they get the question right, they get to put up their X or O. Three in a row wins.
To make a flannelboard version, simply cut four long strips of felt and five or six circles out of two different colors of felt. (These can be used for other games as well.) Or. . . if you don't want to bother making the game - just use a chalkboard or white board.