(Sorry, I just couldn't resist the temptation to use this somewhat provoking title.)
This recent question motivated me to finally ask the following, somewhat dual, question which I've been wondering about for quite some time. My experience is mainly in maths, bit I am interested in the situation in other subjects, too.
Background. I've been teaching maths classes at German universities for several years; the situation over here tends to be as follows:
German undergraduates have to decide about their major before entering the undergraduate program.
There is a single exam at the end of each course which decides about the overall grade. Students who fail can typically take a second exam some weeks later in the same semester.
For first year undergraduates in maths, the failure rate tends to be somewhere between 30% and 60%. It's more or less comparable for related subjects such as physics.
The exams of those students who fail, do in most cases clearly show that those students did not understand central concepts of the course.
My (subjective and possibly wrong) impression of the situation at many places in the US:
Such high failure rates of courses would be deemed inacceptable and thus, failure rates there are much lower.
Course grades are not determined solely by exams; instead, graded homework often counts considerable weight towards the overall grade.
Question. As the high failure rates that I am used to are, in my experience, mainly due the failing students' insufficient understanding of the contents of the course, I am wondering how the purportedly low failure rates in the US are possible. To put it more concisely:
Why are high pass rates considered acceptable for university courses in the US?
Potential reasons. I can think of with several potential reasons. I am unable, though, to check how valid they are since I lack personal experience in the US.
My premise is false: Failure rates in the US are not significantly lower than in Germany, in general.
First year courses in Germany should rather be compared to, say, third year courses in the US, since this is, if I understand correctly, where most maths students in the US start to work with proofs to some extent. If this alone was the major part of the explanation though, I would expect failure rates in the US to be particularly high in third year courses.
A large number of US universities are just much better in teaching their students a good understanding of the course contents.
The average understanding of students in the US is not higher compared to Germany, but universities simply let them pass anyway.
The US approach to choose a major only when several years into the program, has some kind of early "matching effect": students gradually narrow down the subjects in which they take courses, which results in a good fit between students and subjects before the more advanced courses start. (While this "matching" is rather designed as "filtering" in Germany, via high failure rates in first year courses.)
Quite high tuition fees in the US are an economical incentive for students to focus on courses which are reasonably within their capabilities, while this is not so much the case in Germany due to the mainly tax funded university system.