I was a primary TA and worked with SEN children, and I will give you a couple of things that MAY help a bit, but I can't really promise they will:
ONE - An inexpensive and easy to use book, that can encourage children with reading, spelling and writing, and really help them to understand Phonics, is reviewed in the MN Book Reviews section. Just search ‘Phonics’. I think he might enjoy using this book, as it is colourful and entertaining, and easy for children to use on their own, or with adult support.
TWO - When I worked with less able Yr2 children, who were finding learning to read particularly difficult, we often used a SoundWorks kit, which consisted of a set of wooden letter blocks, which the child used to build simple words.? The theory was that, for some children, it is easier to SPELL words than READ them, which is a later stage.
It started with three-letter words, with a vowel in the middle - "a" glued onto a board.
The child then looked at the individual letter blocks, and was asked to make the word "c a t". Then he was asked, how do we change "c a t" into "h a t", which letter do we need to change? Then change "hat" into "ham" (with an emphasis on the "mmmm" sound). Work slowly, and pronounce the sounds accurately and clearly.
So, if you can find or make suitable letters, and make a card with "a" glued in the middle, your child may enjoy building the words. Use letters that are occurring in words in the books he is bringing home, and then go on to make cards for the other vowels if it seems to work with "a".
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Another technique I have used with children who can't write sentences unaided, is they DICTATE their story to me, and I would type it on the computer. They enjoy seeing their text appear on the screen, and often they do have good ideas, but are unable to write it themselves.
So, if you have a tape recorder, or a phone that records, could he dictate information into it, for a story or a description of his weekend, or something. Is he able to assemble ideas in his head, and then dictate them? For many children, the ideas are there, but it is the physical writing and spelling that is the difficulty. If he can then write the words, or if that is too difficult for him, an adult could write or type them.