I don't have any experience with apraxia / dyspraxia. But... I was curious if your son is on any medication? Lots of these meds have side effects and apraxia is sometimes one. My son was on two different seizure meds (started on one, then switched to another) with dizziness as a side effect. They affected his walking - he liked to push around a doll stroller for stability. Once off of those meds, he gave up the doll stroller. Anyway, I can see dizziness affecting writing skills - it can be a vision issue.

If you decide to look up side effects, make sure you find the fda pdf file on whatever med it is. From the meds I've looked up, apraxia tends to be a more rare side effect and it generally isn't listed on every website.