I believe I should respond to "stop" the shooter if I know the particulars, like where, how many, etc.
Going solo sucks, but like you said, you probably gotta go. Waiting to go in ala Columbine gives the scumbags time to play their game. Current industry doctrine seems to be close and destroy.
I assume from your post that you are uniformed or otherwise identifiable so follow up responders don't shoot you by mistake.
Do you have radio comm with your department or the school admin? If you have radio contact with faculty you might sound a select few out to be eyes and ears in a crisis.
If you get to know the teachers and staff you'll probably get a feel for who could be an asset in a bad situation.
Some school administrators have their head in the sand but if if possible you need to get the admin involved in some contingency planning.
Some schools "lockdown" in a crisis; some pursue the evacuation method. In truth which works best will depend on what's happening.
Unprotected students huddled in a cafeteria are fish in a barrel to unopposed shooters.
However students gathered in a parking lot are toast if the attackers have prepared explosives in vehicles.
It really comes down to intel. Most of the schools here have some form of radio communications in place, even if it's just a few key staffers.
It almost goes without saying that once you engage your shooting skills need to be excellent due to the likelihood of panicked innocents in all directions.
I would suggest a lot of work on shooting on the move and use of cover.
Walk the school and preplan cover and angles of fire.
Carry plenty of ammo and a backup gun or two. (In a desperate situation you could arm another good guy.)
Just some thoughts.