One of my favorite books about WWII in high school was a series of reports by the great war correspondent Ernie Pyle entitled Brave Men. Pyle tended to write stories about common soldiers, sailors and airmen, which reflected the everyday war experiences of men who were not concerned about strategic things but how to survive war on a daily basis. If you want to understand how the war "felt" to the average combatant or support troops, Brave Men is a worthwhile read, and because it was written for the average newspaper reader on the home front, is very accessible for a high school student.
I second an earlier comment that Heller's Catch-22 is a great novel to come out of WWII, arguably the finest. Even though some of the comedic elements may seem outlandish to readers, Heller captured the absurdity of certain aspects of military life and WWII better than anyone else has done then or since.
Another favorite is a book written by a young Marine, Eugene Sledge, entitled With the Old Breed, about his experiences in the Marine Corps during WWII, and specifically about the war in the Pacific. Sledge, who was not a professional writer, captures the camaraderie of being in the smallest branch of the services, as well as the horrors of fighting several battles in the Pacific against an enemy that did not seek, or give, any quarter. Sledge conveys the "cognitive dissonance" of coming from a small American town and being thrown into, at the the age of 17 (I think), some of the most violent battles of WWII.
Stephen Ambrose's books Band of Brothers and Wild Blue Yonder, which follow a paratrooper unit invading Normandy and the Army Air Corps, respectively, would be two very good reads, especially for an AP class.