Thanks to everyone for the many thoughtful contributions to the wargaming exercise, begun below. I'd like to summarize the first set of 'lessons learned.' This is only a summary of the broad areas of agreement: there is a tremendous amount of expertise available in the comments to the post below.
Scenario I has prompted two basic theoretical responses, one defensive and one offensive. The defensive response seems rather more popular: that, at minimum, an armed student with proper training and a defensive firearm could secure his own classroom, deny it to an aggressor, and (if an evacuation route were available, as they were at VA Tech) cover the escape of the unarmed. If that can be achieved, the armed citizen is then able to either leave as well, or engage in further operations at the risk of only his own life. He has to make a personal decision as to his capacity here -- for example, our former MP at Ft. Bragg, who notes that he is no longer sufficiently mobile to pursue less static operations, versus our Air Marshal, who is entirely (and doubtless justifiably) confident of his capability.
If there were one such armed civilian in any given classroom, it should be possible in most cases to deny the shooter victims beyond the first place he hits. If there is only one here and there, it would still sharply reduce the number of potential victims, and increase the danger to would-be assassins.
The offensive response notes that, the sooner the assassin is taken out, the fewer people will die. This mode suggests seeking out and destroying the assassin at once. This position is controversial among respondents:
a) Some note the lack of intelligence on the precise nature of the threat, which might not be a school shooter. It could be a legitimate police operation, or it could be a terrorist act.
b) Others mentioned the high level of risk to the armed citizen. 'Clearing a building is a team sport,' notes TheNewGuy, quite rightly. However, one also recognizes that personal survival may not be the point. Referencing Professor Liviu Librescu, we note that defending the weak is sometimes a matter for which we might properly undertake even great personal risk, or the certainty of personal destruction.
Nevertheless, a review of the severity and nature of the dangers ought to be sobering. Anyone undertaking this sort of measure would be wise to adopt 1charlie2's suggestion to inform the police of distinguishing features; the suggestion to expect police communications to be garbled, and thus to be prepared to surrender quickly should they overtake your position. Indeed, in any scenario 1 response, communicating your existence and intentions to the police is a priority, as is making sure they are aware of the situation in case you fail.
The general consensus is that this is a high risk strategy, with a relatively low survival probability. Some of the best trained and most experienced of respondents, however, suggest that it is the right course.
c) For those who feel competent to engage the enemy, there are two strongly supported pieces of advice. The first is from Air Marshal SamTheFAM:
Ten to one odds that guy was target fixated. Hell even after shooting tens of thousands of rounds in training I still chant "Scan and breath" to myself all the while shooting...scan and breath, scan and breath. Because the majority of folks forget to do both. He could have been taken out from behind by a few well placed center mass shots.The second is the advice to track on gunfire, and lay a counterambush on likely points of transit. Whenever possible, leave a covered line of retreat open for yourself.
d) Some respondents point to the danger of shooting other armed students, attempting the same sort of actions. This is a good point: friendly fire is a real danger in these cases.
Scenario II has produced a fairly unified structure. We all seem to agree that the basic structure is as suggested: evade, control, retaliate, or as many of you put it, move, draw, fire. First do what you can to gain a second or two out of the direct line of fire; then, get control of your weapon; then, direct fire to center mass.
Two sideline discussions have arisen.
The first is among those respondants who know they will never be carrying arms. What should you do?
My advice is twofold. Those of you who think you might be constitutionally capable of learning to bear arms, lawfully and with personal discipline, ought to do exactly that. We need more of your kind contributing to the defense of the common peace and lawful order.
There remain those of you who are not confident of being able to do such things. There is nothing wrong with this. You should take the lead of those who are, and follow their directions in getting to the best exit available. Withdraw from the scene as you are able, and stay gone. Contact the police. Not everyone is a fighter.
The second offshoot wondered if the scenarios were valid. If we came to the point that people were reliably carrying arms on campus, at least two respondents asked, why wouldn't wannabe assassins change their tactics and go somewhere else?
There are two basic responses to that.
1) This is not a bug, it's a feature. The point is to harden the campus so as to make it a less attractive target. If that adjusts the behavior of bad actors so that they stop shooting up schools, good.
2) However, to have that effect, we have to get to the point that this is a reliable danger they have to consider. In order to get there, we need to establish an understanding of how to respond to events of this type, and get people to the point that they are carrying.