I was able to make sure I was doing an good job teaching by monitoring the grades of a few of the standout students. If I taught a lesson and then tested them on it, and the "top" students did poorly, I knew I did not do a good job. Believe it or not, this never happened. The top students always did well, and the B, C, D, and E students would fluctuate but usually average out to their usual place. This was NOT because they were "bad students" or "dumb" but because of variables such as lack of studying, lack of caring about grades and school, or in some cases because most of them were ESL (English as a second language), the language barrier held them back. But if an entire class failed, including the top students, I would know that I was not doing the best job teaching a subject, or a lesson.