My wife has a civil engineering degree. There were a number of courses where partial credit was not permitted and the final exam was 2 questions. It was common for students to take those courses 3 or 4 times before passing. Giving a failing grade to only 1/3 of the class might get a professor investigated for making the class too easy.

> High graduation rates are an important metric to administrators. If a professor gave a failing grade to 1/3 of the class they would be in hot water.

I remember practically every single instructor/professor on the first day of class during my freshman year of my undergraduate study said something along the lines of "I have no curves. Your grades depend on you and nobody else. If the whole class does well, everyone can get an A. If nobody does well, everybody can fail."

So I guess this was more motivational to get us to study rather than stating facts?

Failing 1/3 of a class if that cohort is genuinely deemed not qualified enough to pass shouldn't be a problem by itself.

But then it raises questions like "are they really unqualified or is the testing methodology inadequate?" and "why was the system unable to provide the necessary growth to such a high slice of the class?". And then the easy way out is to just cherry-pick which students enter the system at all.

I remember a first lecture when I started my CS studies, where the professor said something like "look at the people to your left and to your right, it's likely that at least one of you will drop out by the end of this year; it's ok, this is not for everyone; if you truly believe this is for you, put in the effort and you'll make it"

1/3 isn't that bad in the late 80s/early 90s at the UT Austin CS department. Only ~30% graduated at the time. The orientation was literally "look to your left and looked to your right only one of you will graduate." They weren't joking!

Caltech did not grade on a curve. I recall one class were half the class failed.

That depends. Some schools actually cap the number of students permitted to continue. They fail a certain fixed number or percentage of students below a threshold, even if the raw score is good.