I quit putting in much effort in 9th grade. Our math teacher was self-described as incredibly lazy, and had students grade their own homework, then he would call out names and people would tell him what they got. After 2 weeks of everyone around me claiming random numbers when they hadnt even done it, I stopped bothering myself, which quickly turned into not doing homework or studying for anything.
Then senior year, I got bad depressed and pretty much quit everything. Strait As first 9 weeks (semesters are what matter, but they sent report cards every 9 weeks), and then everything plummeted after. Slept through every class, and just coasted. Failed most of the classes I didnt need, did just enough to get the minimum credits to graduate. Still feel kinda bad about a networking class hosted by a nearby college, I liked the teacher and my poor performance may have reflected badly on him, but....idk, just could not give a damn.
That said, unlike many posts here, most of my teachers were reasonably competent (some notable exceptions), and the overall student body was fine. Bit preachy, and a handful of redneck douche-bags (I remember a very notable rant from a student in 11th grade, in a class with an openly lesbian student, on how all homos should be hanged), but most of the preppy/cool kids were very friendly.