Good GPA? Wear what you like, except distractions (naked) mean back-of-class seating. Bad GPA? You wear a one-size-fits-all jumpsuit made of faded rose-colored velvet.
Good GPA? Eat what you like. Bad GPA? You get that squishy nutriloaf thing normally reserved for misbehaving prisoners.
Good GPA? You get first choice for slots in sports teams, drama club, choir, cheerleading, and all the rest. It doesn't matter if you suck at the activity. Bad GPA? No participation permitted.
Enforce prom date pairs having a minimum average GPA. Those with the highest GPA can pick anybody. Those at the midpoint can pick the better half of the school. Those at the bottom get only one choice, and will thus need to make nice with the top-performing student.
Good GPA? Wander in and out of school as you please. Bad GPA? You pass through metal detectors, get a pat-down, and are sniffed at by the drug-detecting dog.
Good GPA? Move around and chat with friends during lunch. Bad GPA? You get assigned seating and must eat in total silence.
People will invent new ways to attempt dominance. Brutally crush this for any student who fails to perform academically.