I was the political pro, not my brother. Simply put, after being told of the second crash into the WTC, Bush ought to have promptly excused himself from the kiddies and tended to his duties as commander in chief. That would have been the best political course because it would have been the best choice for the sake of the country in a moment of shock and peril.
(1) Leaving abruptly would simply have provided a different propaganda line for the media: “Pres. Bush rattled before classroom of children, Pres. Bush rushes out of classroom etc.”
(2) Nothing in that first 7-8 minutes would further his “duties as Commander-in-Chief” — a man in his position knew it would take more time than that to gather initial facts.
What we were seeing here was probably the first time ever a POTUS was informed “live” of an initial attack upon the USA with media present (there was no reporting on the first 7-8 minutes or even hours of when FDR learned of Pearl Harbor).
Nothing Bush could do in those first 7-8 min. would have made any difference at all to what was already happening on 9/11, so the only useful “duties” he could perform at that moment was to carry on, think about what might await him outside of that room, and to await a more detailed briefing which was to come.
Put it another way: if he had been anywhere in private at that moment, informed by an aide in total secrecy, there was still nothing more consequential he could have been doing in those first 7-8 minutes.