I was apparently like this when i was younger, i dont remember personally but when i was looking into if i was dyslexic or not there was a questionair that my mother had to fill in and all the symptoms pointed to early dyslexia eg bottom crawling down the stairs instead of walking, i had speach therapy untill i was six (i dont remember this eaither!) i could sound out a word when spelling but would add f's or change s's to f's, i would study my box of words with my mum for hours but then when she asked me to spell them i wouldnt be able to, i would get frustrated, scream, cry and often have tantrums because i could not understand why i couldnt do it!
I hated school work and would cry when my mum told me i had to do it, probrably because i knew i would get frustrated, i would often pull at my hair because i thought it would help my brain work (i was young and assumed that if i did this it would turn it on lol
I do not wish to worry you or say that this is what your son has, i am not qualified to do this but have you thought of having him checked for dyslexia?
Sorry if ive written too much or rambled, hope this has helped a little, please keep me updated, i would like to know how he is getting on.