I was exactly in such a situation. My intellectual capacity (My IQ rating has been as low as 145 and as high as 165, depending on what test was used) was mismatched to the low rate and low level at which almost all teachers taught the classes I was in. My intellect was severely underdriven in school. Result: Utter boredom. Total disinterest in all things school, and grades that reflected that. Despite the fact that I could ace tests on chapters that hadn't even been taught yet, I didn't bother to do the routine work and my GPA suffered for it.
The stupid fucks in school administration, including and especially the school board's prized student psychologist (What a stupid cunt she was!), never ever caught on to this simple truth, that I was spectacularly undermotivated by the pathetically slow pace of teaching that was the norm. Not being bright enough to see the problem, they certainly found no good solution for me, so they tried to stuff me into the catch-all for the square pegs like me known as the "specific learning disabilities" class, even though one thing I was always excellent at was LEARNING...when something was presented to me TO learn, of course. Which was rare enough in the regular classes!
I gave them a couple weeks of spectacular academic performance, just for spite, in their abysmal SLD environment,(I completed the year's full curriculum in two weeks) just to show them that they'd fucked up and still didn't GET IT, and FINALLY that was all they needed. They realized that they couldn't provide a program that suited my special talents and need for information delivered at an incredible rate, so they handed me my diploma early by administrative action and pretty much kicked me out of high school.
If I'd been the highly motivated type to start with, I'm sure I'd have gone into college a few years early, but I've always been relatively unmotivated if not downright lazy. However I do soak up knowledge like a dry sponge.
CJ