Here are a couple key points on inequality and education from my article Telling Time with a Broken Clock: the trouble with standardized testing:

• The strongest predictor of student performance on achievement tests is socio-economic status, which is why it is a mistake to believe that the scores tell us about school quality when really they are reflecting affluence or poverty.
• No school or school system has ever become great without great teachers, but what can an excellent teacher do about a child who needs glasses or is hungry? To say that teacher or school quality is the most important variable in education is at best naive. Education historian Diane Ravitch writes, “Reformers tell us that teachers are the most important influence within the school on student scores, and that is right. But the teacher contribution to scores is dwarfed by the influence of family and other out-of-school factors.”
• Ultimately, great teachers make great schools, but great teachers can’t do it alone – they require the support of an equitable society. If we are not careful, we risk misinterpreting the scores, and instead of waging war on poverty and inequity, we end up waging war on teachers and schools.

Here are a couple posts I've written on inequality and education:

• The problem is poverty
• Is poverty an excuse?
• Education excellence requires equity (two great videos)