More than half of USAmericans can't read to a sixth grade level, what does this actually mean?

Years ago I wrote here using an alt about how I had yelled in public at one of my chud neighbors because he put a trump sign on his lawn. I stalked him later on facebook (which I no longer use) and saw his writing about the encounter. I could barely understand what he was even talking about. This is a white boomer who works as a school bus driver. Becoming a school bus driver now is super hard actually, it requires six months of full-time training/education where I live, but I suspect that he got into school bus driving before all of that, because his writing looked almost like he had just smashed his keyboard with his hands. No punctuation, many spelling and grammatical mistakes. I remember he wrote "I'm" when he should have written "I am"—it was something like: "He doesn't know how nice of a guy I am," but he wrote it "He doesn't know how nice of a guy I'm." This guy also speaks with a heavy accent and only in short, simple sentences. I've worked as an ESL teacher for years, and I tell students now—many of them are perfectionists—that they already speak English better than some native speakers.

I don't know what level his literacy is at. I guess he is barely capable of communicating in writing and also able to sign and cash checks and buy things at the grocery store?

Another story: I work in a blue collar field which requires us to enter about four houses each day. 95% of houses have absolutely no books at all. Of the remaining 5% of houses with books, the vast majority are only bibles and cookbooks. 1% has books that are mostly for decoration. Another 1% or so has books that appear to have been read. I have only found a handful of houses with communist texts. Most of the houses with books that seem to have been read are just filled with liberal nonsense. (One Mormon landlord I met, who owned so many houses I think he was confused about the number, had dozens of Mormon-themed books in his basement, including even one book about overcoming doubt about Mormonism.) A coworker and I once entered the very rare American house that seemed to have hundreds of books. My coworker (white, in his thirties, has a high school education at best) didn't even notice them. I guess I just found this stunning. I was fascinated with the books' existence and wanted to examine them all, even if they were almost certainly all liberal nonsense (the owners were retired academics, one book I remember seeing there was something like "Hitler and Stalin"), but my coworker was still just glued to tiktok on his phone (and not communist tiktok). He's actually an okay guy. He so desperately wants to be a normal American, but he has two trans kids whom he seems to love, so it's basically impossible for him to be as reactionary as he would like to be. I talked with him for about a hundred hours when we worked together, never revealing that I was a communist and always avoiding obvious Marxist language, and only made modest progress at best. When we finished working together a few months ago, he had expressed interest in voting for RFK. He had also never heard of long covid and seemed to be concerned about it when I mentioned it. Then he went back to normal. As for me, I have trouble watching videos to learn things because they're just too slow, sometimes even if I set them at double speed. I prefer reading, although I do listen to a lot of books and podcasts, although I'm usually listening while I'm doing something else. Not to denigrate learning from videos since I know they can be useful and some people really get a lot out of them (especially when it comes to learning blue collar shit), but in my opinion, a random book is going to have a lot more information than a random youtube video.