Well in our personal experience, DS got very very slow last year at everything. We didn't know why- he wasn't always ridiculously slow, though he was always uncoordinated and didn't have fantastic fine motor skills. First his schoolwork was slow then it bled into other things.
Then I watched his class.... and it all made sense. The faster you were, the more boring worksheets you had to complete. You already colored A? Oh goody- here it is in a different font. You already finished your math? Oh goody- here it is with beans instead of corn kernels. Last one in line? Awesome, you get to sit at the end of the bench instead of being squished in the middle. Last one to circle? You get to sit in the back where you can daydream uninterrupted.
I suddenly realized that he had NO reward whatsoever for being fast at anything.
I realize this isn't the case with everyone and that there are certainly kids who are just not that fast. But for us, it helped immensely when I started having a "carrot and stick" approach. "First one to the car can choose the music!" "Last one to the table has to clear the dishes!" Suddenly, he began having a bit of pep and motivation at home.
Didn't change anything at school- we had to change schools to make that happen but that's an entirely different story.