I'm not a bush advocate, but he handled himself in that school like a professional. It took him 5 minutes to finish the story, but he spared the kids an extremely complex confusion that would've perplexed them for who knows how long, not to mention leave the teachers there to calm the students. He invested those few minutes to insure calm amongst the kids, and quickly addressed the tragedy afterwards.
Honestly, would going crazy, throwing down the book, and sprinting out of the room accomplish anything? If he had, partisan left-wing babies would scream about how he showed too little respect for the children and showed panic and little self-control.