I actually wanted to post this to clarify how points about it ought to be made, it’s pretty old and people know about it. Education resources in the USA are really unfairly distributed. It’s not that Americans are so evil because they’re stupid, it’s part of their de facto apartheid state’s continuation. Americans support bloodthirsty imperialism in order to hoard the education funding via property taxes in little enclaves. You’re not going to educate them out of killing you. They don’t care if you watch One Piece, and many don’t recognize this deal won’t be doled out to new generations on the same level, and will always get worse.
Of course, the educated and wealthy Americans are unusually stupid, globally, but I don’t think anyone is doubting that right now.
I’m not really sure what 6th grade level actually means, but when I was in 6th grade I was able to read pretty much anything I wanted to if it was just standard English (like I probably couldn’t understand some paper full of medical jargon or old stuff like Shakespeare, but I could read a novel or a newspaper just fine.)
Before handheld device convenience, my personal experience with Shakespeare/Chaucer/Plato (stuff assigned in middle school, high school (gymnasium), college {university), after a first class coaching for the unit language ~5-10 minutes, and reading aloud/discussion about what the author said in the first few paragraphs, it was fairly easy to catch on fairly quickly, but I did use the college dictionary and a notebook to write definitions, pronunciation, use in my own modern sentence as I went because writing it down helps me remember.
Local newspapers and popular magazines are generally around 5th - 7th grade reading level so they can reach a broad audience.