HEADCANON:
some of the UA faculty have degrees or even phds on the subjects they teach (or others). not all of them, just some. they can teach in different departments, classes, and years (depending on the hours they teach and the number of subjects is how much they get paid also):
electoplasm has masters in physics and a phd in mathematics. he teaches physics in 3rd year in general studies and the department of support in all from 1st to 3rd year
midnight has a masters in arts in history (bc shes a huge nerd). she teaches history in 1st year of hero studies and from 1st to 3rd year in general studies, PR in 1st year of public relations, 2nd and 3rd year of hero studies.
cementoss has a degree in literature, which he teaches in all 4 departments (general studies, hero studies, support, and management), however, the onlt department that has the subject from 1st to 3rd year is general studies, the rest only have it in 1st year
power loader is an engineer and teaches exclusively in the support department (from 1st to 3rd year) and is the head of the department
thirteen has a degree in astronomy but doesn't really use it for school
vlad king has a degree in education, which has really helped for his class to thrive
present mic has a communications degree. he teaches english every year, every department, and teaches communications every year in management
hound dog is a psychologist!
other heros like snipe and aizawa dont necessarily have further studies, so they are homeroom teachers (hc snipe is homeroom teacher in hero studies for 3rd year)
i think not all teachers at the UA are heros, some of them are just teachers, especially the ones we dont see, and those who teach several subjects share are not the only ones teaching them (so like there are 5 classes that have the same subject, one teacher teaches in 3 classes and the other one in two, but teach the same subject) which is the case for midnight and cementoss, for example.