In the big picture it breaks down into the system, the school, and your child. You got to monitor the school system on the political level (school board, funding, etc), be present at the school enough to know when you're not finding out about matters, checking that homework even if completed is actually understood, engaging the child so as to quantify his experience of the teachers and classmates, and the list goes on.
Given that we continue to have a child in an urban public elementary school (his third and favorite, I should interject), I think this 20061126 New York Times article "What It Takes to Make a Student" gets at why I worry about his education and his understanding of the world around him; its review of selected research reminds me why the politicians are stupid to think a better testing student is so easily attainable. The battle is against a multi-faceted moving target. A point not covered in the article, and one I wonder if is explored in any literature, asks about the relevance of nuanced but similarly important concept involving ethno-cultural factors that may eclipse class under certain settings.
How come its so obvious to me that there's not just one way to educate a child. After all private schools have long educated dumb white kids using teachers without advanced degrees; yet, they somehow emerge functionally more competent than their similarly or better endowed counterparts. What the research really gets at is that certain parents don't leave education at the school and however they supplement it in the home makes the difference....more so than any particular school. The whole rigamarole I learned can be quantified as "concerted cultivation". I'd venture to guess it's why you can have the off-the-radar successes of Sudbury Valley types of schools and other alternatives. In the end,
“noncognitive” abilities like self-control, adaptability, patience and openness — the kinds of qualities that middle-class parents pass on to their children every day, in all kinds of subtle and indirect ways — have a huge and measurable impact on a child’s future successThe expectation is a minimal success of graduation and somehow it has to be gotten. (Yes, there are cheaters but...most do finish nominally proficient.) Research coming out of UPenn's Positive Psychology Center characterizes it as tenacity, or grit. Pretty much explains me.
For the meatier version of matters, see "Self-discipline outdoes IQ in predicting academic performance of adolescents" in Psychological Science.