Thank you all for your comments. Very helpful. I am working with him on checking his work. As I work from home, he sees me editing and rereading all the time, and I try to emphasize the importance of checking his work. (Often, he'll say the right answer to a math problem and then write down a different number, or transcribe the answer from the last question to the question he just solved. We are definitely working on these types of attentional issues. I'm always telling him, you know the answer, may as well get credit for it.)
I'm afraid to try the backwards idea, as it may confuse him. Then again, he may get a kick out of it. After all, he likes literal humor and there's nothing wrong with knowing a word "forwards and backwards."
I think I'll just go the route of write a first draft, then go back and reread and edit and I'll help him correct his spelling errors at that point. I think this is an example of his big disconnect with the teachers this year - they teach a certain way assuming a certain level and don't vary what they do for him.
At least he wants to learn how to spell.
