So I'd be very interested in any suggestions as well.
I'm waiting on someone at school to get back to us with some suggestions - though our issues are mainly spelling related for our 12 year old.
At home we've worked through apple and pears books, most of the Spelfabet work books and IXL English word analysis bits and we do everything we can to encourage reading and use audio books to introduce classics and expand vocabulary. All we get told is she spelling is an issue which we all know.
She has always read a lot although her interest has waned lately.
There's no issue with vocabulary or general knowledge. That's why I feel there is plenty of scope to improve formal writing with grammar knowledge and focus on spelling. But this is not going to be on the agenda at school. (We are not in England and have a different education system that my others have been through so I've seen roughly what's ahead.)
I wanted to start something this year while shes still amenable and we are years away from the exam stuff.