Like Biker said, anyone in any way dealing with the reality that the situation is violent and combative, they get my support over all the others who have pie-in-the-sky ideas about how to make things more secure.
Like they said, determined attackers are guaranteed to attack, because they're determined! The phrase 'determined attacker' means that they WILL get past passive security measures. Armed security guards are better than locked doors, but it's not feasible to provide the numbers that would be needed to secure buildings the size of schools.
And as for minimizing the numbers of entrances/exits, that's silly. The most dangerous threat in urban societies is still fire, and it's damned irresponsible to sacrifice any level of fire safety for anything.
What's needed is more officials suggesting tactics and strategies like this text-book thing, until everyone and their cousin realizes that their kids need to know how to survive a violent situation, and act Pro-Actively. This text-book idea could be useful, you tell kids #1 run away from the school ASAP, don't wait for any official announcement, if something starts happening run away immediately. #2 If running puts you or someone you feel like protecting in worse danger, or is for any reason impractical, then attack or defend immediately. Do not try to reason or plead. #3 Use any tools you feel like. If that's a textbook or a tazer, use it.
It's like after 9/11, you had two types of people. Those who started talking about how to ban more items from airplanes, and those who were on TV telling people how to improvise weapons on airplanes by breaking their food trays and such.