Isn't it impossible that 'they' refer to 'the teacher'? I've seen that 'they' sometimes refer to a singular noun with no gender. Check this whole paragraph plz.
Doing any career takes time and effort, but doing music requires you to work harder. It's not a 9 to 5 existence. The first priority is to be a good teacher and to let your students know that you are actually interested in them,
Oh, right. It seems that the author intended the second "they" to refer to the teacher. It is somewhat confusing, because the first "they" definitely refers to "students."