My son will be 12 next month and has severe dysgraphia and dyslexia.
At 9, his writing was illegible, his spelling horrid, and he did not even see the lines on the paper. He'd start somewhere towards the top middle and drift so that by the end of the page he could only get one word on the line because he was so far to the right. We tried paper with raised lines and mechanical pencils with spongy grips, and they helped some. Your comment about using the back of the paper and sideways made me laugh. This happened A LOT with him.
His writing is actually much better after 3 years of OT, but his spelling, punctuation and grammar are atrocious. He does most of his work on the computer - even his math - and sends the files directly to his teachers via email. He has this funky rhythm when he types because he uses spell check for almost every word. This has helped his spelling in his typed words but sometimes leads to some funny word combinations in his sentences since he doesn't really discriminate between there, their or they're, etc.
We had added to his IEP that he cannot be penalized for spelling unless it's a spelling test, and that grammar and spelling are not part of the grade on projects. That being said, I proof his major projects and help him with the spelling, punctuation, etc. when possible.
