Hazrat Muhammad was a teacher if you have some example that a teacher can't read & write tell us.what he will teach if he doesnot know himself to read and write?
Dear Brother,
Hazrat Mohammad (SAAW) was not here to teach a certain language or course or writing an essay kind of stuff.
He was appointed to teach people the system and art of living in a system by setting the examples by doing it himself. I think one can call it teaching by practice.
Now, coming back to my earlier example, These business owner surely in way are teaching us some new techniques, some new methods and /or strategies, although they are not running a school, they are teaching by practice.