I guess the problem for me is an over active mind, I find that it rarely slows down and even at times when I am writing my brain gets ahead of me and I start to write the next word in the sentence before completing the current one...
I have always had a highly active mind and my mother loves recounting a story from my childhood. When I was in the 1st grade my teacher believed that I wasn't paying attention in class as I was constantly doodling or looking at pictures in books. My mother asked her to do a simple thing and when she felt I wasn't paying attention she was to ask me a question related to what it was that she'd been doing or speaking about.
Naturally of course this didn't take long to happen and I got asked the question and answered it correctly. I have no recollection of the entire thing but that is something my mother remembers very fondly because it showed that I was paying attention in class even if the lessons seemed to bore me.