The First Academy Building has a saying above the entrance, "Here boys come to be made men," why is it and its location significant?
The First Academy Building is the building that host the Assembly Room. In Chapter 12, we readers watch a great interrogation offered by Brinker, to Finny and Gene in order to get to the bottom of a mystery. One way boys become men figuratively is being under fire or under the pressure of truth, or reality... which it what is uncovered in that scene in Chapter 12. This phrase given much earlier in the book foreshadows this Chapter 12 moment.
Another way to answer this question is to look at the building as representative of the Devon School. This school is literally a prep school for college, but what it ends up prepping many boys for in this book is the war. Thus, the title A Separate Peace. Many references are made to the differences between 16 and 17, then 17 and 18. Between 16 and 18, boys go from teens to men, and the peace of childhood to the atrocity of war, or the war of life.