Do materials conduct electricity?

It's been a while since I set up an activity for my eldest son in the form of an experiment where he needed to think about what might happen, make a prediction and then test it.  I thought we'd give one a go, building his knowledge of materials that conduct electricity.

I gave him some play dough (play doh brand, but any salt-based dough works), a 9V battery (PP3) with clip (you can do it without, but take care not to short the battery), an LED, a piezo buzzer and a selection of materials of which some conduct electricity.  He started out matching the words for each material that I'd written out with the relevant objects which got him thinking both about what things were made of, and also how to recognise the words when written.  

We then talked about which might conduct electricity (e.g. wires around the house are wrapped in plastic so it probably doesn't conduct, but the wires themselves are metal) and he made a hypothesis by putting the words that matched materials he thought would conduct electricity on a piece of paper labelled "conductors".  

We then talked about how to make a circuit to test whether they are conductors or insulators, and he knew he needed a gap in the circuit to put the material in.  He had a choice of a circuit that made a sound, or that had a light when a conductor was put in, and he chose to make it do both.  I suggested not using too much of the play dough as - whilst it conducts - the resistance is quite high and a long loop of dough would mean the LED was very dim and the sound very quiet!

He then tested the materials in turn, announcing whether they conducted or not.  He was really intrigued by the double-ended pencil and how it conducted, but wood didn't (although I didn't attempt to explain why graphite is a conductor!), and also surprised by just how well water conducted.  We discussed how we need to keep water away from the mains electricity in the house because the water can conduct electricity.

He then did some more experimentation without any input from me, finding ways to put two of the conducting materials into a circuit, and seeing what happened when the LED and buzzer were in series rather than in parallel.  It was fun watching him problem solve rather than asking me for help e.g. when he knew the materials conducted but nothing happened, he went round the circuit to find the break where something had come apart. There are lots of ways of exploring play dough circuits, and I've started exploring some simple ones with his little brother, revisiting some of the things I've tried with the big one over the last couple of years.