rofl, it just clicked with me that this was a "networking" science fair. I guess I just like blowing things up... Sorry about that.
How about a demonstration of wireless network security using wireshark to sniff packets out? Bound to open a lot of people's eyes.
He could do "How Networks work", but I think it might be a bit broad (though I don't know how much time each student has, how long the fair lasts for, etc...). Honestly I think that would be kind of hard (for people who don't know that much about computers, let alone how they communicate with each other) to understand because it could get kind of technical. I suppose if he kept it simple it could work.
I'm actually kind of excited about this. He should film his "presentation" of his project and put it on you-tube so we can watch.
The fair is for 2 1/2 hours. The problem is he forgot to ask if he's allowed to bring in his laptop to hook it up..... so the science fair is on the first tuesday back so he's going to be asking if he can bring in his laptop.... if so he'll do the one freestyler suggested, if not he'll do the how network works one. And Daeva, He's a qualified in Network + He going to have to do both of them xD in like 3 days xD and find out if he's allowed to bring in his laptop on the science fair date xD