Reading one day, not the next?

Hi Wayne and welcome to the forum,

To understand this, perhaps you've had the experience where as you go to type in a pin number or password, that you've been using for ages.
Suddenly as you go to type it in, you're not sure about it?
So then you try again, only to be more uncertain about it? You might have then decided to come back later, or find where you've written it down?
As the harder you try to recall it, the more confused it becomes?
Yet it's not that you don't know the number/ password?
Just something is disrupting retrieval of it?
I've been looking into this for a few years, and trying to observe and understand what disrupts it?
Where basically what I've found, is that as I recall it, a fleeting thought of 'doubt' comes in disrupts it?
But this has a 'snowball effect', where as I try again, I recall the last disrupted attempt, which disrupts the next attempt, and goes on in a cycle?
But then if I go away and come back the next day, having forgotten about yesterday's attempt?
Then I can recall it instantly.
But on the other hand, if I recall yesterday's attempt, it will disrupt me again today.

So that with your examples of 'that,them,same, house'?
The difference is probably that one day he just recalls the words without doubt, so that the words just flow.
But the next day, he brings to doubt to the page, from the first word? Where the harder he tries, the more confused it becomes?

Perhaps it could be explained to him in terms of, 'letting the words flow as he reads'?
Which if you asked him what is difference about the days that he can read at or near grade level?
He will quite probably relate to the words just flowing? Where he gets out the way and doesn't doubt each one?

In my opinion, something else is going on. Or at least, something else as well, is going on. There is also the issue of word attack skills. While a word could "instantly look familiar" to a person who has read a word many times, the ability to sound-out words does not go away. One day, the word THAT would immediately look familiar, but a 7 year-old would normally still know what a "T" sounds like or what a "th" sounds like. Some people would recognize "at" and others would blend a short "a" sound,and/or a long "a" sound with a "t" sound, but people who are progressing in reading would not just have a BLANK slate on one day, and be able to read at a first grade level (for example) on other days. That implies there are no word attack skills or ability to figure out unfamiliar words and that is important even from the beginning of reading, even if people also learn by "sight reading" whole words even without trying (just by seeing the same word numerous times). It sounds to me like a left brain process might not be working well with this child, even though right brain visual perception ability is assisting in the learning of reading. Either this is the case or perhaps he is not being taught how to sound out words, but letters and their sounds should be more constant than the way you described.