As I've said elsewhere my children were 13, 11 and 8 when they were deregistered.
All three have SEN.
One has severe dysgraphia, which is complex difficulties with writing, so would run a million miles rather than take a job that requires a lot of handwriting. She does however write enough to get by in every day life, form filling, list making etc. She didn't do any GCSEs or A levels before going into Adult Education and then onto Uni. She uses the computer to type everything else and her mobile phone contains her diary, lists of things to do etc. She managed to run a small family business where she had started as a Saturday girl, whilst the owner was on Materinty Leave. She did all of the ordering etc, it was writing for a purpose and therefore worth the extra effort.
The dysgraphia hasn't stopped her recognising the need to be able to discuss a subject at length on paper, her critical thinking ability and verbal dexterity hasn't been hampered by not being able to write easily, as she has discussed and debated freely (and very enthusiastically) through out her autonomous home education. She then quickly learnt how to construct essays etc to get good marks in FE College and then Uni level education.
The youngest has been diagnosed as very severely dyslexic and moderate dysgraphia, so couldn't read until she was 14 (she'd left school completely unable to read or spell even her own name) So she didn't really write until she had 'got' reading. It didn't stop her education running ahead though. Her writing speed is still slightly slower than average, but again she writes for purpose-and is writing songs and melodies a lot of the time these days. She too makes huge use of technology-it IS an enormous boon for someone with these difficulties.
She's always said her laptop and now her IPhone have "set her free"
When she was retested at FE college for her dyslexia, she was slightly below average on writing speed, and spelling, average at reading (HOW we danced and cried in delight when we read that) but her comprehension and vocabulary were the highest the examiner had ever come across. Again she constructed essays well-she did an OU starter course and they helped with feedback on essay construction, but said she was already doing well for her age. her assignments at FE college got top marks and she came out with straight Distinctions and top of the class.
Our son (the eldest) doesn't have a problem with handwriting, didn't really write anything he didn't 'have' to when he was in school. However as an autonomous home educator, he wrote when he saw a useful purpose.
He loved Warhammer, and then got into Fantasy Role Play Games, and began to write his own story lines and characters as a Games Master for his own games. He wrote reams and reams!
He's doing just fine now, with his degree. Just yesterday he told me about the last of the second year exams he'd done and said they were brilliant questions for him, he said he wrote plenty, and could have stayed writing about it all day!
We didn't 'make' them do any writing/practise essays-or anything else.
I've known quite a few Autonomous home educators, write stories and now know of one or two have written novels. I know a couple who are disciplined enough to do that National Novel Writing Month
I guess I am trying to say, where the autonomously home educated youngster sees the need/finds the useful purpose, they can and will write loads.