Why is it only the right that get angry about how state schools fail the poor?

Does it matter if the poor are given a bad eduction? Christine Blower, head of the National Union of Teachers, has just been on BBC1 Sunday Politics. She’s very influential (as her £155,000 pay package suggests) especially at a time when Labour policy is aligning behind NUT policy. When confronted with figures showing how the poor achieve far worse exams results than the rich, she had this to say:-

So"that is not the failure of comprehensive education. That is because we have a monstrously unequal society." In other words: blame the parents. Some of these pupils, she says, are in the hands of slob parents who don't give them breakfast. "They may not have a bed in which they can sleep," she said.