"Punctuation then quotation. P then Q"

When i was in the fifth grade, my teacher Mrs. Brown, came up with a witty rhyme to help us remember how to punctuate quotations. It went "Punctuation then quotation. P then Q." My whole entire writing life I have followed that rule without fail. After reading the dialogue chapter in the Nortom Field Guide to Writing, I learned that the punctuation actually does not always go inside the quotations. In situations where you are putting a singular word inside quotations, as in "the so-called 'users'," you put the punctuation outside the quotes.