[feel_the_need]

American here. I took Calculus I in both highschool and college. I thought it was easy in highschool. The rigor of the college course was incomparable. Mostly because the way they asked the questions on the exams were far more demanding.

[balabaster]

That's because in high school you're not really given the whole picture of how to apply your knowledge and you don't have the life experience yet to understand how to use it usefully so while you understand the math in a limited fashion, you don't really get it. By the time you're in College, you're expected to really get it by the time you sit down in an exam and can apply it to the real world. So the exam questions are designed to test if you really do get it or if you're just going through the motions of what you were taught.

[takk309]

Agreed, Calculus I in university is more demanding. I had the fortune of using the same text in high school as in university. However, the difference between the classes was pace. In high school we had class every day and took a week to work through a chapter. In university we had class three times a week and went through a chapter each class. All told it took one semester (15 weeks) at university to cover what took an entire school year (30 weeks) in high school.