For me it was the mid-90s and my sister the late 80s. She had school cancelled on final exam day due to a bomb threat. The first half of 11th Grade, for me, students were put in "lock down"[0] and then dismissed early due to a bomb threat.

When I went to High School the doors were left unlocked during school hours. It was normal for past students to "pop in" during the school day or in the afternoon for social visits to teachers. We had hall monitors who would question why you were roaming the halls if you looked young enough to be a student but a simple "I graduated last year and stopped in to catch up with my programming teacher" was all that was required all but one time I stopped in (they made me get a pass from the office all of once). I'm not saying "it was safer this way" but I often wonder if the increased security -- sometimes approaching "prison security" -- has the side-effect of some segments of the population "behaving accordingly."

There were school shootings "in my day" but those were limited to rough schools in the inner city. They were reported along-side all of the other crime happening "in the high-crime areas of the city", brushed off by most of us.

Weapon policy was much more lax when I attended school. I routinely carried a 3.5" pocket knife to school because I was irritated with dullness of the various wire cutters/tools in my electronics class. My electronics teacher regularly borrowed my knife without questioning "why in the hell a HS student is bring what looks like a switch-blade to school" (I was always seen as "one of the good kids", though).

We lived about ten miles from a large rural High School, as well. I remember picking up a cousin at his school around hunting season and being surprised, back then, to see pick-up trucks with gun racks proudly displaying scoped rifles in both the staff and student parking lots. This was, of course, "prior to Columbine" and I suspect they put a stop to that shortly thereafter.

With news attention on school shootings and not bombs, it makes sense that hoaxes tend to focus in that direction. School shootings get a lot of coverage with the focus then usually shifting to legislation aimed at restricting gun ownership[1]. The issue is that it's caused people to identify "the problem" as "school shootings" rather than "mass casualty events."

Bearing in mind that the perpetrators of these sorts of things are often of the mindset of "taking out as many people as possible while committing suicide", if it were actually possible to "ban all firearms" in the US, the problem would not be solved. As a High School kid who's parents do not/would never own a gun ... extremely conservative, yet pro-gun control parents[2] ... I had no access to a firearm and no clue how I would acquire one. However, the summer before my senior year in HS, myself and a few friends went off into the woods with a pipe bomb I had made out of things from my Dad's basement and "black powder" salvaged from Independence Day incendiaries. We wanted to make "the mother of all M-80s." The device was smaller than most handguns, easy to conceal and easy to ignite. It would have been devastating if exploded in a hallway.

To this day I have never seen such a powerful explosion in person. "Fingers plugging ears" was not enough to prevent dampening of our hearing by 90% instantly. Despite being an "empty pipe bomb" (lots of "powder" but no screws/bolts/other shrapnel), pieces of it flew -- easily -- twice as far as the distance we were standing from it. Had any of us been positioned at the right angle there would have been no time to react and I have no doubt anyone in the direct path would have been killed/injured in a manner at least as seriously as if they'd taken a large caliber bullet.

About the only solution I have heard that would make a difference is "more high schools with fewer students." The school I attended was designed with about a 750-total-student capacity in mind. My graduating class was 850. We were packed into hallways so tight that you basically squeezed your way to class with the running joke being that if you were too tired, just lift your feet off the ground and let everyone else take you there by force. Putting a high-trained police officer in that situation and asking them to "hit the shooter" would be practically impossible. Even assuming they hit the target, the bullet would travel through several other students before its settled into a wall/other sufficiently dense object capable of ending its journey.

[0] Something we didn't drill for back then except for tornado drills.

[1] Which, despite generally being a supporter of second amendment rights, I find myself supporting some of the more sensible approaches. Incidentally, I am not in support of "arming the teachers" -- the probability that adding another gun to the situation won't just result in more students being caught up in cross-fire isn't an adequate solution.

[2] I live in a blue collar community that fits well into the category of "Reagan Democrats" -- so much so that until my late teens I had no idea Republicans were pro-gun and Democrats were anti-gun. Every Democrat I knew was a card carrying member of a union (usually one specific union) and every one of them had a firearm collection of a small militia. Nobody in my family/extended family -- all conservatives -- owned a firearm.