Will the poor always be with us?
Britain has the unenviable reputation for having the worst social mobility of any industrialised nation. What is more, the chances of a British youngster climbing out of hardship are said to be lower today than they were fifty years ago.
Gordon Brown says "the great test of our time" is to change that. But after a year in No 10 he knows there isn't a lever marked 'pull this to get the poorest parents to be more ambitious for their children'.
There are two principal drivers influencing movement up or down the social ladder - our education and our parents.
Labour has targeted resources to help schools in deprived areas and yet the gap between primary school kids on free school meals and others has widened. School choice has aided those most able to play the system while for those able to opt out, Britain's private schools offer the greatest educational added-value in the world. University expansion has also generally benefited the better off, in part because poorer families are less likely to take on student debt.
Ensuring your 'social inheritance' doesn't stunt your growth is summed up in Labour's mantra - "opportunity for all, not just the privileged few". Sure Start, working family tax credits and the minimum wage have also attempted to reduce what the left likes to call "differential life chances". But research suggests a child's ambition and risk-taking are likely to be dictated by family rather than policy.
So how can politicians encourage parents to do better for their children? You can punish bad behaviour: parenting orders, Asbos, that sort of thing - but it can end up making a difficult situation even worse. Or you might reward good behaviour, which is what the prime minister announced today. Hard cash - £200 for parents in some of England's most deprived communities whose children take part in programmes to improve health and development.
However, that too has its problems: those who take responsibility for their children can feel justifiably miffed that others who don't get rewarded.
In researching this issue for the BBC News At Ten tonight I was sent some fascinating graphs (how sad am I?) which show how household income distribution has changed in the UK since 1961. Watch the animation. It becomes clear how relative wealth has improved, but the gap between richest and poorest has widnened. What is really worrying is that those at the very bottom of the income table do not seem able to escape. If anything, their plight is getting worse as they slip further behind the rest of society.
In that short animation is one of the greatest social challenges of our age.