Why is it that magnets cant pick things up through a conductor?

So I have a science experiment I have to do... I'm doing magnet strength. I have a magnet, and it doesn't pick up any of the paperclips through the wood, or the Mild Steel. I need explanations but I can only say that it doesn't go through the wood because wood is an insulator so it can't p through. What about the Mild Steel? I can't explain that one and I really need an explanation. The mild steel is less than a centimeter thick (what's it... a decimeter?) and its 5"x(a little less than 6")All help is much appreciated, spam is not appreciated, if it's not the right answer dont' bother posting please.