Here are some things we're working on with my DS8 that may or may not apply to your boy...
-Hand strengthening exercises using Thera-Putty, tweezers, push/pull exercises, etc.
-Oral spelling, so he can build the spelling knowledge without the need for writing. This is still a considerable challenge for him. We're not sure whether it's just because we've neglected it so long while trying to iron out the handwriting or because of a larger processing issue. The school is supposed to do full IQ testing before his next IEP meeting so we can look at working memory, processing, etc.
-Consistency in correcting his letter formation, spacing, capitalization, and punctuation in his written work, which will expand to include spelling as he's ready.
-Keyboarding skills. We have had moderate success with TTRS (
https://www.ttrsonline.com/), which is a typing program for dyslexic students that is based off of OG methods.
-Speech-to-text, so he can get his ideas out and focus on just subject matter, organization, and conventions.
-And a bunch of HWT.
Several members of his IEP team have decided that there's no hope for him to ever really write legibly, and are really pushing just the Speech-to-Text kinda stuff. I'm not ready to give up that fight yet though--he's only 8. So we keep practicing.