I started by asking them to share what they noticed when building circuits about what part of the wire they had to use, and why. They knew they had to use the ends of the wire to make the circuit work. I asked why, and they said it had to be metal.
I then told them they would be finding out what materials conduct electricity by seeing if they could be used to complete a circuit. I showed them the materials they would be testing, and had them circle their predictions on Insulators and Conductors, and explain their thinking.
I had a student from each table collect their materials, as well as a battery, light bulb holder, and 3 wires with stripped ends. I gave them bulb holders and tape this time so that they could test the objects for conductivity without needing quite so much dexterity to keep it all together. I drew a diagram on the board on how to put the circuit together, but they needed some help setting up their circuits (figuring out the bulb holders, screwing in the bulbs, etc.) Once they had the set up correct, they were able to test each circuit for conductivity relatively easily.
I told them to record whether the bulb lit up or not, but this was a missed opportunity to embed the vocabulary. It would have better better to have them tell whether the material was an insulator or a conductor.
I knew they would need support drawing conclusions about insulators and conductors, so I had a few students share what they noticed with the class. Their results indicated that only metals were conductors, but not all metals. I did show them using a multimeter that the pencil lead conducts electricity as well, just not as well as the metals. I could have put a few batteries together, which would have had enough volts to light the bulb through the pencil, but I didn't really have the time to set it up on the fly.
Finally, I asked them why it might be good to have an insulator. A student came up with "So you don't have a short circuit" right away. I showed them a picture of a Wiring Harness to emphasize that there are many wires in complicated electronics, and insulation around the wire prevents short circuits. They weren't able to come up with any other reasons on their own, so I held up a power cord and asked them why they use insulators on the cord. They understood that insulators keep us safe and out of the circuit.