I like to use The FuseBox to teach 6th graders about electricity. This is a circuit builder game from Northern PowerGrid which allows students to build series circuits. One part that I like is that the game is more forgiving than when students are actually building circuits. Next, when students begin building actual circuits, they will have a better understanding of how they operate, and of some of the problems they may encounter with real circuits. There are three levels to this game. On a side note, there is a bat used in this game, and it may not be intuitive as to how it is used. The bat is used to break the light bulb(s) in the circuit, to see how one broken bulb effects the other bulbs within the circuit. Also note that the speaker that the kids connect, can make an annoying sound in a classroom, so you may wish to have students turn the volume way down, or to mute the volume.
Disclaimer: This game requires Flash Player 7 or newer, and will not work on iPads.