I'm not saying they were completely ignored, but there weren't any histrionics. It was a fire DRILL, not a fire, and we kids just goofed off on the playground. The cops certainly weren't concerned either; they made a cursory check because that's their job.
Fast forward to 2007, I'm working as a teacher at a very large, affluent suburban school, and the *one* time in six years that we got a bomb threat caused absolute pandemonium. Lockdown, class cancelled for the rest of the day, helicopters flying overhead, and a student's diorama (found in a hallway) was treated like a suspected IED. Local news went into hysterics and interviewed concerned parents outside the school, asking them about 911. The next day, attendance was about 50%.
I'd call what happened when I was a kid routine, and I agree with the OP that kids calling in bomb threats was so common when we were growing up that it was practically a cliche. I'm not defending it, and only a really stupid or sociopathic kid would have done it, but it happened and it happened much more often than it does now.
I'd call what happened when I was a teacher insane.