I agree with Lorel, and for that reason I always recommend video (or at least audio) of him doing whatever it is he does that makes you think he's HG+. Get him talking about his passion and record that. I really think that if you see/hear an HG+ kid in action, you know it!
Creative writing and math pages are great, but even better is video of him doing the writing and/or math so they can see his thought process, with the work attached. Not only does this reaffirm that the child is not being coached, it also makes the HG+ness a lot more obvious. Math pages are dead. Video brings a child to life.
Just my opinion...
