Tenshi Koukou

On one normal day while leaving school, Lukio dies from a car accident. Next thing he knows, he's being transported to a school called "Angel High School," where future Archangels study.

With no other choice (being that he's actually dead), he now has to study to become a full Archangel, but somehow he becomes involved in the school's rivalry against the "Fallen Angel School." Now he must study with his fellow apprentice angels and compete against the fallen angel students.

(Source: MangaHelpers)