I'm going to play devil's advocate here.
As someone who grew up in this school district, in the city that Florida lovingly refers to as "Detroit South," where the schools' police officers are ALREADY St. Petersburg/Pinellas Park/Clearwater/Largo/Dunedin/Tarpon Police or Pinellas County Sheriffs, it's not coming across as anything out of the ordinary other than that it has the school district's name on them, instead of the county or city's. I feel this is partially sensationalist journalism. Does a school district need M-16s? Well, it's hard to say. We had riots in 1996, I had to be wanded when I got off the bus to go to school. My high school was known for 2 things: its football team and its rapes. No, I'm not fucking joking, my parents were terrified I went there instead of trying to get into a magnet program. Fortunately, the jaw breaking incident I had in middle school kept boys more than 20ft away from me at all times.
I do not agree with the militarization of police forces, especially school police (MRAPs and grenade launchers? Really California?) but someone did raise a point: a pistol will do nothing in the event of a wackjob coming in with an AK-47.
At a range the length of a classroom, how is an M-16 better against an AK-47 than a pistol? The pistol is easier to conceal and has less weight so it is faster to aim.
On a less sane and more guncrazy note: I think an FN P90 would be better than either. It has the best of both worlds, almost as light as a pistol, more bullets than either and a great firerate plus the 5.7 ammo shoots through bulletproof vests without carrying on after the first body as far as 9mm bullets do.