My ds7 is in a similar boat, not quite as pronounced on regular worksheets, but with timed math fact sheets, he moves at an agonizing pace. And there isn't any oh, well you did 'ok', though not great, it's just a pass or a fail so he was beginning to feel like a failure in math.
I have taken a lot of time to reassure my ds that he
actually is uniquely suited to pursuing and enjoying math, and that memorization of what
I refer to as 'computation facts' will come faster the more he uses them, but I am in no
rush to see him complete a 20 problem sheet in 1 minute rather than in 2 minutes.
Sometimes I show him articles on mathematicians who can't balance their check books, but think things through at a pace which allows them to come up with new ideas about things which other folks have been 'seeing' for decades but not
pondering.
I think the guy who solved Poincares conjecture about the nature of space is a great example. When it first came out, someone stated that it just goes to show you that most of our truly profound thoughts have resulted from long periods of isolated thinking. Newton is another good example of this. Not a bad thing.
http://www.nytimes.com/2006/08/15/science/15math.html
