Isnt walking out of a classroom a violation of civil/criminal "law"? Either penal, and or municipal?
This responsibility lies upon the parents?
Start documenting these non complying students sending notices of such non compliance to the parents to place liability upon them. One student leaving, is one student up to no good within the community.
Place more monitors in school grounds. Have more "guest speakers" who, can speak and maybe be "role models" by use of reverse psychological methods of communications.
As an experienced Law Enforcement officer/Prison officer, I believe public speaking of my experiences will assist with these types of problems, if we were able to get to the students minds, through ways that they are familiar with. Sometimes, these students came from such families and they need to know, "they are intelligent" enough not to be influenced by surroundings.
Disclaimer: As submitted to the Arizona Daily Star.