S.,
it is never too late to get help.
If your son is doing well with reading when there is one-on-one teaching option, then it could be great if you find some help at school, and definitely help him also at home.
I can give some suggestions, as I am an English Language teacher myself, and I also volunteered for the program that covers such issues. There is "America Counts * America Reads" Program. In Universities, they have college students volunteering, who come to schools and help kids like Your son. It is not a disaster, let's say - it's a bummer, but it definitely needs to be paid a lot of attention to, as reading is one of the main sources of learning in every single class: be it science, or social studies, or even technology (computers).
So, do please talk to the teachers in school, and you can even call the nearest University (I do not know where you live), and ask them about this program, America Counts * America Reads. You can also google, and look for info about the help they provide those students who have difficulties. It is a GOOD way to get help, it takes place right in the school, during the school time, at no cost to you; it is very supportive for your son, AND your teacher also. Your son will feel more confident, if he will be succeeding during these hours of reading with the 'helper'. It also has a psychological part to it: see, if he fails in class, he starts thinking that he cannot do it, and quits doing and trying altogether. You do not want it to happen. In every way, support him and say he can do it well, it only takes a little more effort for him, as brain is like computers: oh, tell him this: some computers work slowly, and some are very fast. the slow computer can perform the same task as efficiently as the fast one, it only takes a little more time. His brain is set on the slower mode than some other students' brain, and nothing at all is wrong about it. Many professors and geniuses did not fit into the regular classroom. Do you know that Einstein did not do well is school at all? Please, support him morally a lot, while he will learn reading more efficiently, this is a very important part of the issue, especially at this age, when he starts getting into this teenagers' rebellious time. You can prevent many problems ahead, if You will manage keeping him on the positive side, not all frustrated and drawn back!!!
Now, by the information you shared about your problem, it is obvious that Your son is a VISUAL LEARNER: he sees the picture, and he remembers, and he knows what it is all about, and he is capable of retelling the story, and eliciting meaning of it.
SO, my first advice to you at home is:
let him draw what he reads.
read together one paragraph. Then, take a piece of paper, a pencil (or colored pencils), and do a little drawing. Do not spend much time on it, just stick-figures, some symbolic objects, but so that he has a PICTURE of the paragraph, of what was going on there. Then, move to the next paragraph, and do not read any more, unless the next little doodle-drawing is completed. Do it for every paragraph.
Thus, he will have a set of pictures, maybe comics, and in order to remember, all he needs to do, is to go through his drawings.
Similarly, you can help him even learning-memorizing poems by heart, if needed, drawing pictures for every single word. It takes a little bit more time, but it teaches him to start VISUALIZING the text inside his head.
With time, he will not need to draw anymore, but he will be able to put this picture together inside his brain (mind), as if he actually painted it on the inner screen of his memory-part of his mind...
Do you see what I am saying? This is a little trick I used myself, and helped my own kids, and many kids in class with it.
I am a visual person myself. I have difficulties with math, as numbers are some lifeless creatures that I cannot imagine. In order to count right, I need to see that these are the sheep I count, and better if they are black for odd numbers, and white for even numbers, and even better, if they are soft and cozy, so I could touch them and pet them while counting... then only numbers start making sense to me, Interestingly enough, I loved geometry. Guess why? It is VISUAL! You see what you measure, here are solids, or graphs, or lines and triangles and rectangles and so on.
I do hope you will find a good supportive volunteering teacher's helper in school, and do start drawing at home, please!
It will take time, but you will make it, dear ones!!!
YOU ARE VERY RIGHT TO PAY A LOT OF ATTENTION TO THE PROBLEM!!!
It is important, it needs to be taken care of.
Good luck, a lot of patience, and - go for it!!!
M.