I don't think it's just calculus.  In the Humanities and Social Studies ~ a lot of people get flunked for not having a clue how to write a research paper or to source properly, even though they may had received an A or an B in their courses back in Highschool.

In the case of Math – I have never had a live instructor who could actually teach it.  Online courses feel more effective to me but ultimately I find the best way to learn Math is to find practice problems & solutions on the internet for the course in question.  Even if you are lacking in the logic skills in Math, you could do what the Asians simply do and memorize every problem pattern out there.

Memorizing patterns is technically what people do to pass the LSAT for Law School. .  Math is honestly no different. .  If you do a thousand Calculus word problems online, you will probably end up running into them again (since no one creates their own problems anymore or they only changed the names) on an actual test.