Like everything there are multiple problems. Parents not taking a role in their children's lives and education is widely believed to be linked to a child underachieving in school. At the same time, the most involved parents in the world won't have an effect if a child doesn't care or is otherwise distracted. Drugs, gangs, or other distractions can nullify any effect the parents have. Finally, if a school is unprepared for its students, the students have less of a chance to succeed.
That said, in any great environment some students will not succeed, and even in a poor urban school riddled with violence and drugs some students will rise to the top. What needs to be done is to realize that ALL of these factors come into play. For the part of the government, the schools need to be equipped to provide good teachers and a safe environment. Parents need to be aware of their influence and effect on their offspring. And students need to be aware that high school is not just a place to kill time, but is a test to get into a good college or vocational school that will dramatically increase their chances at a financially comfortable and secure life*.
Blame lies in all parts, perhaps not equally, but certainly not exclusively.
Edit: On that topic you can extend these thoughts to why private schools are better than public schools (on average). The students who go to private schools need to PAY. If your parents are paying, they usually want results... and have probably passed that feeling onto their children. They are more likely to be interested in how their child is doing when they need to pay directly for it. The school gets students by providing a good environment for the students; this includes rejecting problem students; a selectiveness public education does not have.
At the end, it still means that parents are a large influence on their children's success.
Edit *changed phrasing due to driftwood.
Edited, Jun 30th 2009 12:44pm by LockeColeMA