Stand and Deliver
It's your basic "encouraging teacher gets through to unreachable students" stories that gets shown in public schools every once in a while; along the lines of "Dangerous Minds," "Renaissance Man," "The Principal," and "To Sir, With Love" (feel free to name others).
Of these movies (from what I remember of the ones I've seen), Stand and Deliver is the most obvious about bashing the audience over the head with it's societal commentary. The students only fight their teacher minimally, and otherwise are accepting and willing to learn. Thus, the fault of their inadequet education lies not within their own mindsets, but instead is entirely a product of society; They aren't flawed, the system is.
Still, the characters are developed well enough that the audience is invested in them, and that makes up for any lack of originality in the plot. The teacher's humor and sarcastic way of talking shows how much he cares, and it's worrying when he suffers from a heart attack, because its cause is partially the fault of the stress from his teaching job; a job that he's only doing to help out his students.
My favorite line from this movie was said by the "bad boy" of the movie, upon entering class late (after everyone but the teacher has left), right after the teacher has given a sort of inspirational speech about what they'll be trying to achieve in his class.
Angel: Hey, I'm the first one here.
Angel: (sees the board) What's cal-coo-lus?
Though this is "based on a true story," it's a bit embellished. If you're interested, wikipedia has a nice description of the real events that took place: