TEACHING IS AN ART OF COMMUNICATION.
A good teacher is not the one who has lot of knowledge, but the one who knows how to communicate that knowledge. Teaching is about communication!
I've seen many times situations in which some teachers are very proffesional and they know everything about a subject, but it happens that a high percentage of their students fail in a test. Why??
Well, some people might think it's because is a 'tough subjetc' and students should pay more attention... But I don't think so.
When there is a high percentage of students failing in a same classroom, usually it's not because of a lack of interest, but because of a serious communication problem. The teacher and his method are failing.
Unfortunately, when it happens, the teacher is not humble enough for doing this necessary self-criticism's job , and he just prefer to think that their students are lazy.