Let's keep in mind who the adult is supposed to be in this situation. Bender was a troubled kid with crap parents. Crap parents were a recurring theme here with all the kids in detention. Bender acted out and that's not ok. Maybe he went back to his criminal/punk behavior or maybe not. But he did learn something about himself and his peers that day. Perhaps someone who chooses to be a high school principal could make some efforts to teach or inspire the students instead of determining that their futures are predestined based on a sample of behavior in high school. None of Bender's behavior justified Vernon's threats of violence or his viewing of the personal files. In the 50's and 60's students were much more behaved in school because the parents would likely beat, or at minimum make the kids' lives hell if they acted out in school. In the era that this movie was made it was obvious that an underlying theme was that the parents were either checked out, overbearing or trying to live vicariously through their kid. None of those parenting styles are in the best interest of their kids growing up to be confident, productive members of society. Over the years you mention, it has only gotten worse on the parenting end in my view and lo and behold, kids are acting out in more and more disturbing ways. What I liked the most about the movie was that despite all of the adults in their lives, these students were discovering important things about life anyway. By spending that day together, they were able to find common ground, get out of their comfort zones, and realize that they have some control over their lives just by changing their perspectives about themselves and the people around them. That is how most of us have to eventually find our way in this crazy world.