I was in 9th grade english class. Announcement came on saying that a plane hit the world trade centers. Not very specific (did not state there were two planes), so I immediately thought of the 1945 incident when a B-25 bomber hit the empire state building.
A few hours later, in history class, I learned that both towers collapsed and it was a terrorist attack. And although history happened at that moment, we continued on with early european history.