After we had managed to grasp the idea that apostrophes are used to blend words (do not becomes don't), we started walking through the murky waters of elisions and it's vs its. By the time we got to possessive singular and possessive plural their eyes were glazed.
But, I persevered: we talked through some examples and did some together on the board.
Then it was time for the quiz. I was confident. We had covered it thoroughly. Surely in the 10 seconds that had passed they couldn't possibly have forgotten...
As a writer, I know the importance of punctuation and grammar. I'm not perfect myself - but I try.
Some days, being an English teacher can be the most frustrating thing in the world.