A lot of what you described sounds like my ds13 who is dyspraxic and has fine motor dysgraphia due to his dyspraxia. That said, it could be any number of things that are causing the symptoms you see, and it's most likely going to take a complete neuropsych eval to *begin* to tease out what's up. I don't want to sound discouraging, but with complicated kids and these types of symptoms that can be attributed to quite a few different types of issues, it sometimes simply takes time to fully understand what's up.
I'm guessing the reason the first neurospych wasn't conclusive was possibly based on age and maturity - some of the things you're seeing may be developmentally on target but your child is on the late side of the developmental curve, and some things may make more sense once your ds has been in school longer and you're able to see how his schoolwork is impacted. My ds had symptoms of dyspraxia dating back to his very first year or so of life, but we had no clue he was dyspraxic until he was diagnosed in 2nd grade (by a neurospych).
Re diagnosing Disorder of Written Expression - I suspect he's just not *quite* old enough or far enough along on the academics curve for that diagnosis yet. My ds had a DOWE diagnosis in 2nd grade, and later lost the diagnosis (even though he still has reversals in his writing etc)... he lost the diagnosis when his performance on one of the WJ-III Achievement Tests (for writing) score improved in 5th grade. Sooo.. just a guess... but I'm wondering if your ds was young enough that a low score on a similar test wasn't considered significant yet compared to NT developmetal expectations - just a guess. It certainly sounds like he's struggling with writing.
Another thing I'd wonder about is vision - has he had any type of vision exam?
He seems to coordinate new physical skills better than or at least equally to others of his age in his extra-curricular classes.
A note about dyspraxia (not saying that's what your dd has but just for info) - it impacts different people in different ways, and it's not necessarily global in extent. My ds, for example, struggled tremendously with handwriting when he was your ds' age, but he was able to draw absolutely amazingly intricately detailed pictures. The key in understanding your child is to look at the specific skill involved - handwriting requires a different type of brain-hand communication than drawing, for example.
The other thing about dyspraxia is no two people impacted by dyspraxia are impacted in the same way.
Would you mind posting your ds' WPSSI subtest scores, and/or what testing/survey/etc was used to determine he has ADHD? We might be able to help you with some more feedback/thoughts/etc if we had that info. You also noted he's mostly the "HD" from ADHD - it might be helpful if you could describe that in more detail.
Best wishes,
polarbear
