Thank God for the teacher who stayed late to help you. They probably didn’t get paid for that hour.

An hour given after the working day has ended is outside the arrangement. Nobody required it or recorded it, and they did it because they decided your problem was worth their evening. That kind of thing is easy to accept without noticing, because teachers staying late looks like part of the job. It is not part of the job.

Think of the one who did that for you and say so, in words, this week. An email, a note, or stopping at the door on the way out. Tell them what specifically changed because of that hour.