Bush was visiting a Florida classroom and the incident, which was caught on TV film, and has often been used by critics to ridicule his apparently blank face.
"My first reaction was anger. Who the hell would do that to America? Then I immediately focused on the children, and the contrast between the attack and the innocence of children," Bush says in an excerpt of the interview shown to television writers on Thursday.
Bush said he could see the news media at the back of the classroom getting the news on their own cellphones "and it was like watching a silent movie."
Bush said he quickly realized that a lot of people beyond the classroom would be watching for his reaction.
"So I made the decision not to jump up immediately and leave the classroom. I didn't want to rattle the kids. I wanted to project a sense of calm," he said of his decision to remain seated and silent.
"I had been in enough crises to know that the first thing a leader has to do is to project calm," he added. — Bush explains slow reaction to September 11 attacks: