"Explaining that is so simple:"
Really? You have an interesting definition of simple.
"1. Parents either don't have the skills or the time to assist their kids in succeeding."
Bluntly, then they shouldn't have kids -- but I don't think that's the issue. It's very difficult for a diligent single parent to 'assist their kids in succeeding', never mind one who's more apathetic.
"2. Less resources in inner-city schools."
The problem wasn't as as terrible in the past -- when they had less resources. Maybe there was less single parent households?
"3. Poor attitudes towards learning amongst the kids (see item 1)."
Yes -- and see my response to item 1.
"4. Poor teachers: Because teachers in these inner-city areas do not get paid more than their colleagues in good districts, only the worst teachers will teach there. Also, as a teacher, where pay is determined by test results, would you work in an area where the dice are stacked against you (see items 1, 2 and 3 above)?"
Alot of it is based on union tenure in many districts. Also, some districts are just too large (LAUSD, for example) and should be broken up.
The fact is that more an more we as a society are abdicating parental responsibility. Schools have become "food" programs where kids get 2 of their meals a day. Many are open over the summer just to provide food. If the answer is to feed kids where the parents CANT then I think we're scratching the surface of what the real issue is... Maybe we need discuss taking kids away from parents who cant or wont provide for their kids vs. the alternative of raising an ever increasing population of people who cannot or will not take care of themselves and bring in to the world children whom they are not equipped to provide adequate care.