Hard work and the ability to produce the wright answer produce A's at the calculus level. You can get straight A's and still not understand some of the fundamental basis for what you are doing. The mechanics of derivating, intergrating, and the change in the graphcal representation is the main lesson and the regurgatation of those mechanics is what gets A's. Of course this is all relative to your learning style.

Did you take buisness calculus or analytical geometry calculus? The math is the same for both but they take a different approach and have different application.