BTW I “blithely ignored” what you wrote because you wrote that “it’s about 31 hours a week equaling a ten month salary of $20,134.50”, which makes no sense. A salary by definition is not made up of hours. I also find it difficult to believe that anyone in NYC works for so little.
Now here’s a wild guess at what is happening at this unnamed and possibly hypothetical school. Perhaps they used to be paid a salary for ten months; $20K for ten months is above the federal minimum. Perhaps the school has now decided to spread that salary over twelve months instead of ten, and is unaware of the federal minimum. If so, it would be appropriate for one of these salaried employees to bring it to the school’s attention.