I remember it vividly.
I was walking from first block 7th grade algebra to American History with a bunch of friends, cracking jokes, we were all laughing as we entered and were immediately "shush"'d by the teacher, who was sitting, staring at the TV, on which was the image of the twin towers shortly after the first plane had hit. We all sat down in the dark, in silence and watched in horror as the second plane crashed into the buildings. The teacher then simply went "America is under attack," and later continued to say something like "from this day on, your lives will be different." We didn't know what to do. Reports kept coming in about other crashes and rumors about carbombings outside the white house and stuff - we didn't know what to think and we didn't know what was right and wrong. We then saw the Pentagon crash live and were further terrified, but things really hit home when the final hijacked flight crashed in Pennsylvania, our state.
The bells rang like normal, but we didn't really know what to do. So we did what we always did. We went to the next class. Not that anything was different... Except that the teacher (a real prik) refused to turn on the TV for the first 30 minutes of class during which we all just talked about it. Eventually she gave in and turned it on after I had a jog to the bathroom and observed the image of Osama Bin Laden for the first time on the TV screen in the neighboring classroom. I came in and said they found out who was responsible, so she turned it on, then informed me that "Oh, that can't be. They always blame that guy."
From there, we all ate a somber lunch and, for whatever reason, actually played sports in Gym class. I guess that really just expresses the dumboundedness everyone felt. We didn't know what to do, so we just did. All day. Almost all of us were chomping at the bit to grab an automatic weapon and a helmet and fly to wherever necessary to kill the sonuvabitch responsible. But we couldn't. We were 13.
And I think that history teacher was right. I don't think I will ever forget that moment. It'll always be right near the front of my mind.