For me middle-school was stressful hell with every class assigning like 2 pages of homework and you had 6 classes a day, and the teachers weren't the greatest. For me in high-school it's much less stressful, you only have homework for what you couldn't finish in class, and there's only 4 classes a day, and the teachers are awesome
it varies depending on schools tho
for me, the most stressful thing were that my older friends were being total richards to me throughout the whole year, so hopefully I get none of them this year in my classes.