The NY Times recently ran an article on the "Education Gap". For children's school performance, it used to be race that mattered (unsurprisingly, given rampant racism and segregated schools). However, gaps based on race have narrowed. At the same time, the gap between students from rich and poor families has grown: it's now DOUBLE the gap between blacks and whites. This gap continues throughout education, into the college years, meaning that children from poor families have an immensely difficult time succeeding in later life (since college completion is so key to upward social mobility).
So what causes this gap? Interestingly, it is not school spending (which has climbed every year, especially for poorer/less advantaged students, and has become more equal between districts in recent years). Instead, it seems to be parenting.
Rich parents not only outspend poor parents (they spend nine times as much per child), but perhaps more importantly, they spend much more time cultivating their children's minds. By the time they are six, rich children have spent 1300 more hours exploring the world (this doesn't mean traveling necessarily, just visiting anywhere not home or school) and 400 more hours in literacy activities.
Rich people parent differently in other ways too: they talk a lot more to their children. A child from a professional family will hear something like 11 million words in a year, while one from a family on welfare will hear 3 million. They also encourage their children much more, interact with them more, and use more positive reinforcement. In general, their parenting is better by every measure.
By the time rich children arrive at school, they are already at a huge advantage, and the gap only increases over time (both because they are more able to learn, and because they continue to be exposed to more learning opportunities).
The sad thing about this is that talking to your children (or taking them to the park) is free, and so shouldn't need to be limited by socio-economic status. The fact that it is, and therefore social inequality perpetuates itself, is very depressing to me. Maybe mandatory parenting classes would be a good idea?
NB: I use the word "rich" in this post as a shorthand for "someone of high socio-economic status", which usually means educated and employed in a professional occupation. Not everyone in this category is actually wealthy (especially if they work in the nonprofit sector, live in an area with a high cost of living, or have made deliberate choices like having one parent at home which affect income). However, regardless of their income level, they are "rich" in other ways (in particular, their ability to access resources, their educational level, etc.), which is why I use that word here.