But your college courses seems to be so high quality. How does a student in the US go from what sounds like quite a limited education in maths at high-school to doing so well in maths at college? What connects the two up?
Calculus I is differentiation. Calculus II is integration. Calculus III is vector calculus, with stuff like curvature in 3 dimensions. Differential Equations would be the next class.
The AP test covers differentiation and, optionally, integration. It's the first semester or two. This is what a good high school student will do unless the school itself is really bad or really small.
This is the original poster's point. There is no consistency. Even in university. Some schools use quarters, some semesters, some trimesters. Some have letter grades, some percentages. Some are pass/fail freshman year, but are graded in subsequent years (e.g. MIT). What makes up "Calc I" at university varies tremendously.
Nowadays, I think she was right: university students should be ready for university-level work. Many people aren’t at that level the moment they graduate high school. The US really doesn’t have a place for those people, aside from remedial classes.
But, anyhow, for many people, there’s an intermediate step that doesn’t get talked about.
they went to private schools or, alternatively, they went to the wealthier public schools which teach these sort of courses, although usually on a 'tracking' system which segregates the 'smart' from the 'not so smart' at around 12/13.
for the US university (at least the more elite ones):
the above, in combination of the fact that a big chunk of the of the students are international students.
The rest don't even bother, if they go to college at all.