My school in Australia has never had any major threats when I was there except for this one.
A year 9er was angrey because a year 12er had took his skateboard (now remember, this is just what I heard). The Year 9 student smashed an empty classroom window, took a peice of sharp glass and went around trying to find the Year 12er. He didn't find him because, maybe, the Year 12er was a study period or something. The Year 9er kept going to class rooms and storming in until he was stopper by a teacher and, though the teacher got hurt, was disarmed. Now, this was taking place just before lunch and they didn't think to call a lockdown? But then again my schools messed up.