I'm exactly the same way! I also cannot do math in my head. Everything has to be written down. I was helping DS study for a science test the other night and was telling him he needs to write down his vocabulary to help him remember it. He actually didn't need to do that at all; he already knew it. I HAD to write down everything. But, I graduated with honors from both high school and college. You do what you have to do. My step-father put me in a very small private school after struggling in a public school. My academics wasn't the reason for the move; it was more for the fact we were zoned for a very poor district. But I thrived in that kind of environment (very small class).
I can do math in my head, but first I have to convert the problem into a mental image. I do the same thing with language... that's why I've already forgotten an unusual name the moment it's been said, because I can't "picture it." That's also why immersion language software is a failure for me.
I didn't need to write everything down in school, but once I went on to higher learning, I found myself taking notes for the first time, and what I noticed is that I usually didn't need to refer back to notes... the simple act of writing it down had cemented the information in my mind. So there's another giveaway.
Also, whenever we're having meetings to discuss system design (I'm in IT), I'm known as the guy who invariably ends up on the white board to draw out my ideas.
