My younger ds (14) was/is similar. 2 years ago we started 'typing dictation.' I would dictate the book to him and he would type it out. This is not SWB dictation, this was/is spelling dictation. I correct spelling word for word, and I purposely mispronounce the words to augment the correct spelling. This technique is called "think to spell" in SWR. We don't do a lot of rules, because he knows them, but cannot apply them. The problem is a lack of automation. He can spell cat, but at age 12 would have to sound it out, and this would happen with every.single.word, and if it was irregular or there were multiple acceptable representations for a sound, he could not get it right.
So at age 12, we started with Cat in the Hat, to make sure he could master the top 100 words. We kept with it for about two months. So 30 minutes a day and about 200 words at that point. Next book, was Frog and Toad I think. We slowly built up with books he liked and now he is using Eragon. Each book is slightly harder in spelling, plus each book uses different words. He currently mis-spells about 10-20% of the words in Eragon, and can now encode at about 15-20 words a minute. I say 'encode' because if he is typing while looking at the text he can type at 40 words a minute. The problem is not typing, it is the encoding, the spelling.
DS was identified as Dysgraphic, but scored at the top 80th percentile for spelling. (haha) The test was for spelling regular, made-up words. Basically a test of if he knew the rules, but that is not the problem. Spelling for him is just not automated. He had to sound out every single word which was crazy slow and he would forget what he was going to say, and at least 50% of the words would be spelled wrong. What he needed was just *more* practice spelling. So now in addition to his compositions for WWS once a week, he does an additional 200-400 words a day through dictation. We have come very far, and he is very motivated to continue.
Ruth in NZ