any power that could effect every student an teacher/official at the school i would consiter A class. super strength would be B cass, as would super speed and such. anything that easily effects a large city is consitered S class, a country is SS , and a world spanning/effecting power or greater would be SSS... thats how i see it...
so.. from what i can tell... the avg lvl of the entire student body is about C class... and the avg lvl of the teachers and gov would be possibly A class...