Have you considered Fudge the rpg? It uses a scale of difficulty with special "Fudge" dice. The beauty of the system is the fact that the trait levels can be renamed however you want. One suggestion to support the school theme would be to change them to grades, as below

F = Terrible
E = Poor
D = Mediocre
C = Fair
B = Good
A = Great
S = Superb

If you don't know what Fudge is, here is the link.

Grey Ghost Games Site

"The world is your arena now, Sagat, not the street!"
M. Bison, Street Fighter: The Animated Movie