Yes, your further description sounds more like the writing issues have their origins in ADHD/EF/organization. Handwriting is just not that exciting. =)
My #1, who would probably have been referred for ADHD eval in many school systems, had excellent grades in handwriting while in the tiny private school that actually taught that, and is also an exceptional writer and speller, BUT, presents with awful handwriting unless specifically instructed to self-monitor, or especially motivated (such as when creating posters, cards, or hand-lettering artwork). Back when handwriting was a relatively new and interesting task, we had lovely handwriting (cursive was a particular love), but now that handwriting is merely a tool for language expression, we don't care about it at all. Handwriting in math improved only after enough incidents of self or others mis-reading numerals, operations, or signs. Plus, now that proofs are a part of our math, the communicative value of written math work has become more important.
Oh yeah, and tiny handwriting and a desire to save paper (trees!) was also an issue for us.
