"If beatings like this happened more often, there would be fewer teachers hurting our children. "
This is an undeniable truth. If people knew that they would be accountable instantaneously to their neighbors, instead of the slow legal apparatus that is designed to operate dispassionately it would make child molestation much less frequent, and in the most egregious cases, repeat offenses most unlikely.
Often we crow about letting justice prevail, but even justice recognizes "crimes of passion" and treats them less severely than premeditated acts. If caught and prosecuted for this beating, I doubt there would be serious consequences for the perpetrators - and there is an argument, a good argument that this should be so.
Whether right or wrong, beatings like this have the desired effect on society.