How can parents not teach their children to read?

In light of this doentary "Waiting for Superman" that highlights our "awful" public school system it seems that they want to focus on the downfalls of public education. Sure there *are* downfalls in the system but what I want to know if how a parent can know (or maybe how can they not know), their 12 year old is illiterate and not do anything to help them. Do parents really sit back and think it's the school fault alone? Would you never think to sit with your child and read with them and teach them yourself instead of expecting volunteers to come to the boys and girls club to read with them? Do flash cards? Whatever it takes? How can people see their child is failing and not DO something except point fingers at the school where the teacher has to "parent" and teach 30+ students who were never taught to respect authority??