Towards the end of the series / books, the overall tone and culture of the school is closer to that of one during wartime. The possibility of getting blown up can be a bit of a dampener on romantic outings.
In a comment on the same answer, Peteris makes the opposite claim:
Wartime' and the related fear, emotional stress & pressure would generally be an accelerating factor, making teenagers reach emotional adulthood (or the conviction that they have reached it) faster. In such a situation it would be far more likely for teenagers to experiment, and less likely to postpone or restrict things. "Going off to war" - in either literal or figurative sense - is a powerful instinctive reason to have sex now, while you still can. I won't dig for citations, but both biology and historical evidence (say, during WW2 right before war went over those places) supports this
Is there historical evidence to back either of these claims?