University must not be easy for slackers. Slackers must fail in class, or they will not learn the real-world lesson that underlies it all.

As an undergrad, I was a keen student. I listened, learned, and put hours into my homework to really make sure I learned it. I took three courses where around 75% of the class failed or dropped out. I learned an incredible amount of material in those classes, and I aced each of them. I observed my classmates treating the classes like any other, phoning in the homework and getting slaughtered in exams. Each instructor had a prepared speech for day 1 setting expectations for the difficulty of the course.

You get out what you put in. Yes, bad and ineffective teachers exist, but in my experience those teachers are the most generous with grades. The tough ones, willing to fail anybody who doesn't know the material, have the highest standards for themselves as well as the students.

If you really want to know how effective a teacher is, you can't just look at the grades in their class. You also need to track their students to the classes which depend on that material.