First floor, especially problematic, shooter can work from the outside, breaking in through a window to thwart the metal detector. Once inside, the first responder, using one (or several?) swipe cards can
1.) activate partitions, automatically activating police/SWAT GPS connections
2.) activate cooking oil baptism in front of and behind the shooter (no carpets allowed here)
3.) activate shooting port in the partition
4.) activated partition activates warning signal in all classrooms and offices, giving the rest time to unfold the kevlar screens in their classrooms which also automatically locks the doors (unless over-ridden by a swipe-card holder)
If two teachers are manning different partitions (the shooter is between two partitions (along a hall, for example) and catch the shooter in a crossfire, there is little chance that one teacher will hit another (the ports are miniscule), and leaves opportunity to catch a window to the assailant even with "hostages" around.
Whatever happens within the partitions, the shooter is irreversibly captured.