How is he getting on with reading and Phonics?
Read to him as much as you can, including books which might seem too 'old' for him, but explain the meaning of new or difficult words.
This is what I did as a primary TA:
When reading harder books with a child, get him to point to words as he goes along. If he knows the word, or can sound it out, he can say it. If he doesn't know the word, he can hover his finger over it, and YOU say the word for him. Don't stop to analyse or discuss the word at this stage, but try and keep the 'flow' of reading going. Review difficulties at the end, if you wish to. This way, he has the satisfaction of reading more difficult books, without the fear of getting 'stuck' on words.
Hopefully, as he is exposed to more words, some of them may 'sink in'.
Also, try to read (to, or with him) books that have a greater purpose than just the story. I call these 'value added books', and these are good examples:
For able readers, I always suggest Arthur Ransome - “Swallows and Amazons” being the first of a dozen or so books. The stories are quite exciting, with a good sense of 'place' and history; and you could learn to sail from them, too!
I particularly recommend “Coot Club”; set on the Norfolk Broads, it can be read in conjunction with the Ordnance Survey 2-1/2inch map of the Broads, as every place mentioned in the book is real, and even today, is there on the map.
“Watership Down” is another book set in a ‘real’ location, that can be easily found on maps, and on dedicated web sites. The housing development that destroys the rabbits’ original home, exists today on the outskirts of Newbury, Berkshire.