Devon School is a complete contrast with the world at war that was outside of the school's boundaries during the time covered by the main story of A Separate Peace. Gene recognizes, even as he was still a student, how different his existence was from that of boys who were only slightly older than he but were no longer protected by their student status.
As Gene, Finny, and the others come across campus after their first experiment with jumping out of the tree, Gene's description of the scene sets up the contrasts. They walked across "healthy green turf" instead of muddy battlefields; the air "shot through with the twilight sun" instead of flying bullets. The only sound of firing they heard was a "gymnasium truck" backfiring in the distance. The bell tolled to mark the time, not to recognize another fallen fighter's memory.
The faculty, perhaps unwittingly, also recognized the contrast and handled their boys more indulgently than would have been done had it not been for the circumstances away from Devon.
we reminded them of what peace was like, we boys of sixteen...I suppose we could be thought of as a sign of the life the war was being fought to preserve.