I've said this before somewhere, but :
The apostrophe is being used only in these cases:
1) to form possessives of nouns
2) to show the omission of letters
3) to indicate certain plurals of lowercase letters.
In this case, you have plurals of nouns, so if you want to say that something belongs to teachers, you will say:
e.g. This is teachers' room...
Apostrophie goes after s, unlike in singular:
This is teacher's room.
Dod I maybe get your question wrong?
I am not a teacher.