Hi, it looks like the one I'm talking about! Grab yourself a copy and have a good look at the word families and compare to whatever Oxford Reading Tree he's bringing home. Each ORT has a word family and introduces new words as well as drawing on common key stage words (and tricky words as well as comprehension).
I would read aloud his ORT book first, with him listening & following each word and picture as you go. This will ensure he hears the words pronounced correctly, gets a feel for intonation and flow, character expression etc. You should do this one time only, you're not there to read for him, but its a technique you could use a few times and then wean off.
Ensure he reads with a strip of card under each line that he is reading, sliding down the page as he goes. If he is particularly struggling then he should finger point each word as he reads. You should record any errors. Two or more errors, the stage is too hard, full fluent reading with excellent expression the stage is too easy. You can make a spelling list from the word family you find in the book and orally test his spelling at the end. Again, if there are 2 or more errors - you have a word family to focus on for a week (testing orally, daily, give him this as a written test at the end of five days). If the words are mastered continue with the next book and so on. If there are two or more errors after this you will need to consider the ORT stage below and the word family that is in that book.
The idea would be to keep going until you reach 100% spelling, and complete reading fluency with that stage/book and move on to the next stage.
I warn you though, having children undertake extra work all the time & any reluctance on their part severely undermines the learning experience and will cause more harm than good in the long run. You need his agreement to do this and his willingness, you may well want to find some type of reward that he can have if he does the work (not the 100% - the WORK). He should not be badgered or find this method negative. You should work in minutes per year of life, 5years = 5mins, then a break for a snack or play and return to complete anything unfinished but again for the 1min per year rule. This will maximise concentration and prevent you from going 'over'. If he finds you stop after short bursts (5mins) it won't seem quite so awful.
You should be free from distractions, other children & chores, do this somewhere quiet and heap praise on for every little thing, even if its just trying. A negative comment can only be made right with 10 positives. If he responds to stickers, use them - whatever way you can have him see that he is making progress.
Lastly at this stage he should know the names for the letters of the alphabet and the phonic sounds separately. You don't want him to lose his phonic knowledge which should help him sound out unfamiliar words but he should be able or at least start to use the letter name when spelling.
pm me if there's anything further I can help with, good luck.