My son has been using the Susan Barton Reading & Spelling program since his diagnosis in 2013. We are more than half way through the program! He has become a better and confident speller. Yes, he still asks me how to spell things, but I am amazed at how much more skilled he has become.
I know this is not the only program that works, but it has to be explicit, systematic and multi-sensory.
Here is a link to what the International Dyslexia Association Recommends:
Ligia
