I was presenting a library orientation lesson to a 2nd grade class, when another teacher came in and asked me to turn on the TV because "something terrible was happening in Manhattan." I turned on the TV and turned it away from the class and watched the horrible events out of the corner of my eye while giving a cheerful lesson to the children, as other teachers came in.
Of course we all thought it was an accident at first and then we saw the second plane. We remembered that we would be able to see the towers from the library window and watched in horror as the second plane struck; we saw it in a kind of double vision from the window and on TV.
By then the children were aware that something was happening and asked what was wrong. Since we really didn't know the ramifications at that point, we said there was a very bad fire in Manhattan.
It was after the children returned to their classroom with their teacher that we heard about the Pentagon, the crash in Pennsylvania, and saw the towers collapse.
The rest of the day was tense. Several staff members had family who worked in the towers and we waited in fear until we heard that they were safe. (Later we would find out that several staff members had lost friends, or the sons of friends.) The office staff were fielding phone calls from frantic parents needing to be reassured that their children were safe, and of course many parents came to school to take their children home. We had to firmly insist that they behave calmly so as to not frighten the children.
The principal and any teachers that could, would stay until every child was picked up. The last child was accounted for at approximately 6 p.m. with many tales of escape on foot from lower Manhattan and long travel delays.