My grades varied in high school. I'd be making Ds in at least half of my classes all throughout the semester, but I always managed to pull those Ds up to Cs before they got put on MY PERMANENT RECOOOOORRRD (transcript). I suspect this was not always my doing, though. The other half were As, always in Math, but otherwise all electives that I took because they were easy or interesting, and there was the occasional B. Somehow wound up with something like a 3.5 GPA.

College was another story