We've all played connect four as children, sliding those red and yellow discs into that flimsy, blue frame. And I'm sure you've all played it in class, either with the actual, physical version if you are lucky, or on a board.
Now you can play a digital version with your class! Simply split your class into two, equal teams and assign each team a colour (red or yellow). Then, if they answer your question correctly they can place their piece. Have them touch the left side of the place they want to occupy to place a red piece and the right for a yellow piece. Bearing in mind that they can only place pieced on top of existing pieces, not in mid air! And, of course, the winning team is the first team to get four pieces in a row, either vertical, horizontal or diagonal.