Evidence of unfair teacher allocation

I heard an interesting factoid today: in Pennsylvania a few years back, teachers took a test in their subject area (I forget the name).  It wasn't a very hard test, but nevertheless, 30% of the teachers failed it.  That's bad enough, but this is far worse: 70% of teachers in the city of Philadelphia failed!!!  What dramatic evidence that low-income minority kids are systematically given the least qualified teachers!  (But don't tell that to the author of that Forbes article a month ago, Gapology 101, or James Heckman, the economist who published the Op Ed in WSJ around the same time -- they prefer to blame the victims and toss out misleading statistics to argue that demography is destiny.  It's NOT!)