If you took a look at the old textbooks, you’d find that at the same grade level, students were learning much more advanced material even a generation or two ago.
I was in beginning grade school exactly two generations ago, seeing that my grandchildren are there now. Well, my oldest grandchild is in first grade, and is getting “advanced addition” already. i.e. multiple digit addition. She hates it. I really don’t remember any school arithmetic before the middle grades, when we were learning long division, but my overall impression is that I had it easier. Could be it was just easy for me, but I really don’t think the schedule we were on was as pressing as it is today.