This site was shared by a member of one of my homeschooling groups some time ago and I think its a gem.
They have textbooks in Arabic for grades 1-12. They have Islamic Studies, handwriting, math, science and a few other subjects. I think they are great if not for the actual subject content then for Arabic studies to practice reading and comprehending Arabic.
As with anything, review first before sharing with your child. There is a nice little Islamic Studies curriculum, but I have not read through the whole thing and even though its from a Muslim country, well of course you still have to be careful (the books are from Palestine).
I was really impressed by these overall. The files are PDFs. Definitely check this out if you can.
Link update (11/25/2012) http://www.pcdc.edu.ps/arabic/indexbook.htm
(However after reposting this link I see that most of the links on this new main page are broken, sorry for the inconvenience.)
If you don’t know too much Arabic, you can hover over the file names and see the subject of the file in your status bar.