The zero tolerance policies in schools are a little bit effective at keeping the schools safer and preventing bullying and violence.
However the schools are not that much safer when they use zero tolerance policies in schools because students will still break the rules regardless of the zero tolerance policy.
Some kids and teens may purposely break the rules of the schools so that they can get expelled from school so they will not have to go back to school.
My brother used to break rules in school on purpose when he was 10 years old so that he would get banned from the school.
Eventually it worked and he wasn't allowed back in that school but could go to another school however our mom chose to home school him instead.
Still the schools today are still having shootings and other violence and bullying even with the zero tolerance policies.
So the zero tolerance policies are not 100 percent effective at stopping rule breaking and threats however the zero tolerance policies in the schools do help somewhat.