It's not a common phrase, but it's not uncommon either. A p.v. is one in which the "winner" loses so much that he might as well have lost.

Example: One nuclear power quickly dispatched another yesterday, but nattering nabobs from the winner's surviving city considered it a pyrrhic victory.

Regarding the movie: I have not seen it. But there are places where the education system is definitely weird. There are tons and tons of rules to keep the good students in line, but very little can be done to get rid of dangerous ones, or focus the ones who just need a little help. The success of a school is measured in part by how long it's been since they had a knifing, or how low the failure rate is. I was reminded of this a few weeks ago. During a tutoring session, a very large student threatening undertones to a girl over some excruciatingly minor episode. A very large component of the problem is that one cannot actually honestly discuss the issues without running into charges of racism, elitism, or what have you. There are all kinds of ways of obfuscating meaning that it's almost impossible to communicate. It's no wonder so many of my tutors quit in disgust after a short period of time.