Southpark really nailed that last season.  First episode was everyone making fun of Karen for freaking out about school shootings, until eventually she accepted it's just normal Americana like Baseball and Apple Pie.  The rest of the season, every time the kids were shown in school there were shooters and swat battling it out and everyone just ignoring it.

It's a testament to how adaptive we are.  When I was in grade school, we had yearly moments of silence for Columbine.  That was *the* school shooting.  Now, it's so normal that students aren't allowed to put their exam on hold to take cover, real-life Southpark episode.