“Rather than consider noncognitive capacities as skills to be taught, I [have come] to conclude, it’s more accurate and useful to look at them as products of a child’s environment. There is certainly strong evidence that this is true in early childhood; we have in recent years learned a great deal about the effects that adverse environments have on children’s early development. And there is growing evidence that even in middle and high school, children’s noncognitive capacities are primarily a reflection of the environment in which they are embedded, including, centrally, their school environment.”
Source: It’s the Environment, Stupid « Annie Murphy Paul
This is pretty obvious in hindsight, there has always been a strong correlation between poverty and school performance. When a student spends a third of their day at school it will also have an effect.