electronic help for spelling issues

I’m searching for something that will help my dyslexic son with his spelling.  We are using All About Spelling and Spelling Wisdom and it is improving.  However when he writes a letter or a narration he still has problems and I need to spend lots of time helping him correct.  We bought an electronic thesaurus thinking that would help since it said it could be used for spelling.  It is not helpful at all.  If he doesn’t type the word in correctly, it gives him a completely different word.  Does anyone have any suggestions about a product to help with this?  Thanks,

Jean