As a teacher's pet all through high school, I sympathized every day with my teachers, many of whom started out with idealistic expectations but were never able to come into a classroom and just teach. I never understood why kids in my classes could not give the teachers the basic respect they needed to do their job.
In "187," I recognized those teachers in Samuel L. Jackson's Trevor Garfield, a caring teacher who wants to help but continually gets rejected, until his frustration turns into a desire for vengeance.
Students in today's schools have way more power than the teachers do. The most a teacher can do is get a student in trouble academically, while the students who are stirring things up have already so lost their way that they don't care, and will resort to using savage tactics on those they perceive to be holding them down.
By the time a decent high school teacher gets to them, the most troubled kids are so bitter from years of neglect that they can't -- or don't want to -- believe that anyone cares about helping them. The wall of frustration that has been built up on both sides must be broken down before any teaching can be done, a process that is so long and emotionally draining that both teachers and students usually give up before any real work can be done.
In most movies about frustrated teachers in inner-city schools, the teacher is ultimately able to reach out to those students he deems diamonds in the rough, getting through to them with innovative teaching and one-on-one attention until his caring is reciprocated. In "187," the opposite happens: Garfield gets so fed up that he decides the only way to get respect is to resort to his students' methods.
I've seen both teachers and students get abused for a really long time, and I hate to say it, but in my eyes it happens to teachers more. It's easy to see how a teacher could be driven to violence: The good ones watch the ideals they seek to instill get shot down every day in the faces of those they want to inspire.