Answer:

The basic idea of the battle room came to me when I was sixteen. My future sister-in-law, Laura Dene Low (she soon married my older brother, Bill), had urged me to read Asimov's Foundation trilogy, which blew me away. I found myself wanting to come up with a futuristic story myself, and my rudimentary understanding of science fiction at the time led me to assume that sf stories began by the author thinking of a futuristic idea (and it certainly is one way to come up with a story).

Since I had been a Civil War buff for years, and because my brother Bill was in the army at the time (and the Vietnam War was at its peak), I speculated on how military training would be different in the future -- especially war in space, when there were three dimensions to think about. It wouldn't be like flying airplanes, because in flying there's always a "down" to orient yourself with. It would take drastic rethinking of the organization of objects in space and time . . . and so I came up with the battleroom as a means of training soldiers for 3D combat.

Years later, when I wanted to write a story that was completely and obviously science fiction, I came back to that idea and realized that if the soldiers being trained were all little kids, the story would be much more powerful. But this, too, came out of the obvious truth that most of the time our soldiers are children, or we make them into children through training -- we want them utterly dependent on their commanders for their understanding of reality, the way children are utterly dependent on their parents.