Mid-line processing.as long as you do not ask him to codify it into left or right... but if he has to copy a geometric pattern that is in front of him, it will take him ages and parts of it will be wrong and/or very slipshod.
Read more: http://www.conductdisorders.com/forum/f6/we-have-some-answers-53576/#ixzz2RgA5CQqZ
If you have to cross over between right and left, or specifically make both coordinate... it becomes complicated.
And it seems to affect fine skills more than gross skills.
Thus... the cases of highly athletic kids who have major problems with writing, reading, art...
I've also heard/read somewhere that some skills use predominantly right or left brain - but skills that really make both sides of the brain work together can be harder for some of us (and writing is one of those skills, in particular)