Does teachers have an apostrophe at the end of the s or before the s?

There are three possible options for your question. If you are referring to more than one teacher, there is no apostrophe (teachers). If you are referring to an object that belongs to one teacher, the apostrophe is between the r and s (teacher's desk). If you are referring to an object that belongs to more than one teacher, the apostrophe is after the s (teachers' break room).