OK, which is the cause and which is the effect? LeTendre and Baker say that
"The more school systems produce a set of academic winners and losers, the more likely they are to create an atmosphere leading to in-school violence. This does not mean that nations should stop trying to raise scores, but they should be careful to raise the performance among all students. Persistent inequality in national resources produces both long-term and immediate problems for nations, the most pressing of which may be school violence."
I haven't read the book, but the the Penn State press release doesn't indicate how they tried to distinguish causes from effects, and they seem to rely on student evaluation of how violent a school is--which is a bit unobjective, to say the least.
I wouldn't rule out the theory that both violence in schools and inequity in performance stem from the same source. In this country you can very plausibly argue that an aggressively anti-establishment subculture (which I call a "ghetto subculture") drives both school violence and degraded performance. So which do you try to deal with first? Do you try a zero-tolerance policy for school violence? Do you try to hire more teachers (oops--they don't like being attacked in the halls either)? Do you try to address the underlying cultural conflict between civilization and barbarism?