I'm 44yo now... my great grandmother was a school teacher starting in the 1930s, and her 5th grade books for English alone was far more difficult than anything I had through H.S.

What kind of book, grammar, literature? What made it so difficult?

"5th Grade English" a lot of the content itself was centered around proper use of grammar. In practice, these days, it feels like nobody really cares.

It doesn't help that most prescriptivist poppycock is flat-out wrong, either.