Ha, my school straight up bell curved the grades for most classes at the TA level so that a certain number of kids were always going to get a D/F both of which are not passing grades and thus requiring the student to either retake it or switch majors. I myself had to retake 3 classes to get through it and I have had to explain it to one of my parents clients whose son is in the program and has now retaken his 4th class as a junior.

It was pretty brutal but also highly effective at getting me to really study the material to stay above the curve and pass.