S.H.
Have you tried "Kumon"?
LOTS of children, all ages, use Kumon...as in going to a class.
At my daughter's school, they even have one on campus.
It has been greatly favored by many parents that I know... and their children have learned a lot.
Have you asked his Teacher what she can suggest...both professionally AND personally??? In school and outside of school? Try...
here is a link about it:
http://www.kumon.com/
Here's some other links, per my daughter's Teacher:
http://www.littleclickers.com/write.html
http://www.littleclickers.com/skills.html
http://www.littleclickers.com/
The other important thing is to just read to him, or have him read to you, as much as you can. It is so integral to their overall understanding of words and spelling and reading competence.
All the best,
Susan