My cousin is a custodian at a 1500 student suburban high school. During a recent discussion he outlined various school security measures including, among other things, ingress blockades and lock down procedures. He then went on to tell me that the phys ed coaches and students routinely block the rear door open during class so they won't have to use their keys every time someone needs to leave/reenter the building. Makes you feel all warm and safe, doesn't it?