In my country there is a list of mandatory courses for each year of education. All vets-to-be in this Uni or college will learn this, that and that. Same with any other profession. With each year it will be more specific. For example I'm an Ecologist and after the third year of education I decided to specialise in Human Ecology but there still was a list of courses to study mandatory.
And from what I get in USA in college students can choose what courses they want to take or even the professor to be taught. Also they can pay for separate courses. How does they knew that they learned enough and there is no blanks in their education?