I had to check back in my diary in order to get the exact details. Turns out I hadn't really forgotten anything.
I was in 10th grade at the time, 15 years old. Any other day. As soon as my friend and I got off the bus that morning, another friend of ours ran up and told us that a plane had crashed into the WTC. Just from hearing it that way, I immediately assumed it was an accident.
My first class was Algebra II, and it was soon interrupted. We spent the entire time just watching the class TV of the live events. I think I might have missed the first tower collapsing, but I distinctly remember the second falling. It was weird. Once we knew the first tower had gone, it just seemed like a foregone conclusion that, any minute now, the second would as well. And the way Tom Brokaw stated it at the moment it happened seemed like he was holding the same frame of mind. Like Warbler said earlier, it was eerie knowing that you were watching thousands of lives end on live television.
I can't recall if 1st period lasted longer than normal, if the schedule was thrown off at all, but we did eventually go to our other classes. I can't recall any real work happening, though. We continued to watch the TV and talk about it. I remember all the rumors flying around. Someone seemed to be under the impression that Pakistan had claimed responsibility for the attacks.
It wasn't until I got home from school that afternoon that I first heard the name Osama bin Laden. And I pretty much just watched TV the rest of the evening. And according to my diary, I felt some annoyance when I heard the local kids playing outside as if this was just some ordinary day.
Interestingly enough, I also accepted my first date that night. A girl from another school had asked me to her homecoming dance a few weeks before, and, being the hopeless, scared loser around girls I was then, I put off giving her an answer until unprecedented human tragedy goaded me into growing some cajones. Sadly, that didn't really go anywhere in terms of actual romance, but she remains one of my closest friends to this day, so that's good at least...