Teacher slaps student, why?

When a teacher slaps a student, it is an expression of frustration.  Frustration is the result of an incongruity between the teacher's own sphere of influence and their far larger sphere of concern.

It concerns teachers that students misbehave.  In particular, teachers are concerned when misbehaving students interfere with learning by other students.

Teachers have too little influence over student discipline.  The consequences they are allowed to impose are inconsequential, in especially for chronically disruptive students.

Nobody knows how APS teachers feel about the state of student discipline in general, or about chronically disruptive students in particular.  We don't know because the leadership of the APS has never asked them.  There has never been a survey, link, where APS teachers have been asked;

1. what do you think isn't working, and 
2. how would you fix it?

Why haven't they been asked? 

Why haven't teachers, who between them have a hundred thousand years of teaching experience, been asked for their input?

They haven't been asked because the leadership of the APS doesn't want to document the administrative failure to enforce discipline policies.

Once again, stakeholders are unaware of the issue because the leadership of the APS and the establishment media are in cahoots in an ongoing coverup; the Journal, KRQE, KOAT, and KOB.