Other than arithmetic, nothing strikes fear into the hearts of former grade-schoolers like GRAMMAR! Loosely categorized as Language, such subject matter taught us how to diagram a sentence, identify a modifier, and un-dangle our participles! Along with its cousin, phonics, which helped us learn to read the confusing English language and begin our long journey into the written word, grammar still confuses us with archaic rules and contradictory guidelines, not to mention, who can remember all that stuff?
Most of my books are from the 40s and 50s, the Language book on the bottom right of the top photo, was the same one I used in the 5th grade in the early '60s. Brings back so many memories! (click on any of the photos for a closer view)