The problem stated in the original post is not unusual.
During more than 16 years as an elementary school teacher, my experience has been that perhaps roughly 5 percent of my students read on grade level.
Expensive programs such as Kumon are supplements for what USED to be done is school by teachers, and is now in some cases prohibited, teaching phonics for example.
When assessing a child's reading ability, make sure it is done by someone with adequate language arts skills. A baboon will probably think the least literate among us is the next Shakespeare, so his/her assessment should be considered accordingly.
I quit teaching American kids more than a year ago. There was a classroom in our school used by a program called Beyond Basics, if memory serves. The people that worked there, including the person running the show, so to speak, had adequate verbal communications skills, but no specialized training or credentials in education. What they were doing is basically teaching phonics, using materials provided by the program.
What's wrong with this?
Before white women married to powerful, well to do men started getting Ph.D. degrees and writing books about education, TEACHERS used to teach phonics as a matter of course. Policy makers were convinced by these people that teaching phonics- essentially learning what sounds letters make in conjunction with other letters, and various other basic rules of decoding written language, was the reason for our dismal literacy level as a nation. They promoted the "whole language" approach, which is light ( I am being kind ) on learning the rules, and heavy on bombardment with literacy of all kinds and at all levels, an immersion model, if you will.
I returned to the classroom during the pandemic. I taught social studies, among other things, to students in grade 4. The reading level was so abysmal that I would regularly engage in choral reading with students (I read a sentence or two, the class repeated what I read). Doing this long term helps develop not only sight recognition of words, but also reinforces pronunciation conventions relative to the written word. I did this because assigning 2-5 pages for reading was an exercise in futility.
In order to test them, I would write 5 questions from the reading and lectures on the smart board.
I learned very quickly that they not only had trouble reading the questions, but the vast majority were UNABLE to formulate a cohesive sentence in response to any question. I had to allow them to provide pictures for answers (e.g. in order to show the concept of a surplus, when discussing economics), because most simply lacked the skills to respond in writing.
They couldn't do it. Period.
It did not help that many of my colleagues were masters of ebonics, and typically conjugated the verb "to be" as "he be, she be, we be."
I actualyl sat through TWO staff meetings with an ebonics slinging, highly paid staff specialist who decided on her own that pronouncing words correctly was tantamount to discrediting her culture.
I quit out of disgust because we are stupid and lazy as a nation.
As we all know, when America gets a cold, black folks get the flu.
Do the math. If you can.