Unless you have to mention WHO you are teaching, it is usually understood. For example, the word 'student' is redundant unless you are referring to a particular group of students, because anyone who is taught something is a student. It's sort of included in the concept "to teach". So for example, you could have the following two conversations:
- What do you do for a living?
- Ah I teach in a primary school.
- Great! What do you teach?
- I teach music.
- So, what are we going to teach them when we take them on summer camp this year?
- Ok, well you teach them English, and I'll teach the students (them) music.
The latter case refers to a particular group of students, and even then we tend to say "them", because again, 'students' is automatically understood by using the verb 'to teach'.