A quick note, since the question has come up more than once.
Students newly arriving at Shadowfist High School are freshman. They can be sixteen to eighteen, but their physical age has nothing to do with their starting year. Generally, anyone older than eighteen is on their own, and won't be accepted into the school. Once accepted, they will endure four and a half months of being a 'first term' freshman, and then four and a half months of being a second term freshman. At every term, they will undergo a potentially lethal final exam. Once they've completed two exams, they are promoted to the next grade. They have a week of down time between semesters, and then the cycle starts anew. A senior who started school on their sixteenth birthday will be nineteen on the day they graduate. Those who started later will be presumably older.
Also, the school is arranged much more like a college - there are dorms for each grade level, and a small amount of businesses which serve the students. These include bars; there's no prohibitions against students of any year getting drunk. (Post final celebrations are fairly legendarily debauched. Teenagers + alcohol + a literal stay of execution) None of the shops require compensation of any kind; they offer their goods to any student who wants them, but a student who consistently had behavior issues will have this privilege restricted.
Classes don't have 'grades.' While plenty of students compete to be the best in their class, all classes have a simple pass/fail basis. Teachers issue grades as the course goes along, but these are mostly to entice students to shape up, or expect to die during finals.
Finals are not competitive; each student is evaluated separately, and they are not made to kill one another. Adversaries are played by robots, golems, and the occasional summoned demon. Drivers don't race one another, martial artists don't fight one another - though they do PLENTY of that during the course of the semester. It's strongly believed by students and teachers alike that competition with strong rivals is one of the best ways to ensure survival.