I didn't understand what was happening at first because the teachers were just leading us through the normal routine. One of my weirder friends told me the WTC had been hit by terrorists and suggested that we might get out of school early. I was somewhere between having no clue what he was talking about and thinking he was joking. In the next period, they turned on the TV and made announcements over the PA system. TVs were on most of the day... I remember watching it in homeroom while people chattered. We were all really young, comparatively; I was 12, and my classmates mostly 13, I guess. It didn't hit most of them, even after they saw the news. Only people with relatives in NYC or in the army seemed affected at all. The teachers were another story.
I was teary and distraught, guilt-ridden, etc., but that's typical.