And I can relate as the kid. Within the last month or so I was asked to get ketchup out of the refrigerator, and I must have looked right past it a dozen times before I finally found it. I never eat ketchup. It was a new brand (new to me, at least), stored upside down, and she'd peeled the label off of it. You'd only have to glance at it to know it could only be ketchup, but since it didn't look at all like the image I was hunting for, it went ignored completely. My brain didn't even register its existence.
If I don't have any image of what I'm looking for, it's even worse. I'll ask her for details, and since she's the only non-visual person in the house, her descriptions are woefully inadequate. If I ask her where to find a new product she'd bought, I'll get, "It's in the cabinet." Okay, that eliminates less than a third of the total storage space in my kitchen. If I ask my daughter, I'll get, "It's in the pantry, second shelf, behind the popcorn, in a green bag."
Anyway, when your son is dealing with this, I find that the coping mechanism is this: stop. Searching for something with this visual mode can be very quick and efficient, but he has to recognize when it isn't working, and do something else. He has to then switch modes of thinking and become very methodical, organizing his search in a pattern so that every option gets looked at closely, eliminating every option until he's found the right one.
So if he's looking for a paper, an appropriate method would be to take every sheet out of his folder, look at each one-by-one, flipping them over onto the desk until he locates the right one. And if he misses it... do it again.
