I still can't think about the towers without seeing the jumpers in my head and the emotional torment of those awful, heart-rending images hasn't abated one iota for me (also a very old person). Last year DS7, then 6, was comparing images of the NYC skyline and asked me why the towers were in some pictures and not others. Even the abbreviated explanation I gave him caused great anxiety. He ultimately dealt with it by recreating events, complete with lego towers and planes, in a parallel world wherein only the terrorists died, but his initial response was absolute denial that anything bad had happened. And that was just a picture of absence, not of the act.
Your son's ability to discuss his feelings with you in such depth is wonderful and bodes well for you helping him through emotional issues, and I do think home is the place for addressing them. I would, though, mention to the teacher at the conference (assuming no further videos of this nature in the meantime) how distressing you, as an adult, found those particular images. It may be that they are such a part of his accumulated memories of 9/11 that he hasn't stepped back to consider their impact on new viewers. I'm actually quite torn between feeling that the jumpers are inappropriate viewing for that, or maybe any, age and worrying about watering down horror such that children are left with only a partial picture of events.
