This the my viewpoint I acquired as a student, which can be used directly as an answer to this question or to shape your own opinion.
There are teachers who actually show in their everyday interactions with students how they enjoy more teaching those students who are considered to be the smartest of the class (which are, in general, the ones who obtain the best grades). Generally, is much easier to sucessfuly transfer some knowledge to those who are willing to learn something than to not motivated or uninterested students. But actually, this second part is one of the most complicated and most important tasks of a professor, being able to trigger the interest of all the students in the room, provided that they might have very different profiles, in terms of abilities, interests, socioeconomic or cultural backgrounds, etc.
Nowadays, this principle has become one of the crucial aspects of modern education systems, and it is called inclusion. Same lesson, diverse audience and diverse methods in other to reach all of them, so that they all can achieve the same learning objectives.