This book is for parents who have a choice about what kind of school their children go to and find that the choice raises moral dilemmas. Many parents have little choice. They can't afford to go private, or to move into the catchment area of a better state school. Their children are not judged clever enough to get into schools that select by ability. Those in this position may find the book's emphasis on choice irrelevant and elitist. There are, indeed, worse things than middle-class angst. Lots of parents who do have a choice don't find that it raises moral dilemmas. For them it is obvious that parents can, perhaps should, try to get their children into whatever school will be best for them. They will buy their way out of the state system, move house, put their children in for scholarships, hope they get into grammar schools, without even a twinge of conscience. They may find it hard to choose. Lots of different factors have to be taken into account, information has to be gathered, fine on-balance judgements have to be made. Any decision is likely to involve a fair amount of hope and guesswork. All this is difficult enough, but the difficulty is not moral. The focus here is simply on which schools are indeed 'best' and what strategies for getting children into them are most likely to succeed. Those who take this view may find the book's emphasis on morality bizarre or pious.

Parents aware of the moral issues raised by school choice face different problems. Where others worry about which school will be best for their children, they agonise about whether they are justified in seeking the best. They think there is something wrong with an education system that permits children's chances in life to be influenced by their parents' ability and willingness to pay. They disapprove of an arrangement in which the most able and motivated children are creamed off, depriving the majority of the benefits of their ability and motivation. They believe in equality of opportunity, and recognise that it restricts what parents should be allowed to do for their children. They worry about the fit between principle and practice. Must someone who cares about equality of opportunity send her children to the local state school, however unhappy they may be there, and however poor its results? Does consistency require that she not even move into the catchment area of a better school? Or are people's political views about how the system should be - about the kind of options that should be available to people - irrelevant to the choices they make when confronted with a range of options decided by others?

This book, then, is about hypocrisy, about what it means to practise what you preach. The progressive middle classes have always been vulnerable to the charge. People who claim to disapprove of private health care go private. People who say they would be willing to pay more tax don't voluntarily give to the Treasury however much extra money they claim to be keen to have forcibly extracted from them. We all know about champagne socialism. But it is around education that these questions arise most often. That's because equality of opportunity is both a hugely attractive ideal and one that seems to conflict with another legitimate concern: parents' concern for their children's well-being. I started to think systematically about all this during the row attending Harriet Harman's decision, in 1996, to send one of her sons to a selective school outside her local borough of Southwark, apparently contradicting the Labour Party's policy of support for comprehensives. (Her elder son already travelled some distance to the London Oratory, the Catholic school attended by Tony Blair's sons.) Harman was then the Shadow Secretary of State for Education and her decision was bitterly criticised by many of her colleagues. The Guardian reported a fellow-member of the Shadow Cabinet as being 'shocked and disappointed. This is all about the selfishness of the middle classes'. Gerald Steinberg, the chairman of Labour's education committee, resigned in protest, writing that 'As no senior member of the party has felt it necessary to condemn her actions, it is left to lowly me to express my disgust and outrage at what she has done'. Media commentators had a whale of a time - the Spectator ran a column called 'Yes, We Have No Convictions' - and Conservative politicians were quick to accuse her of gaining for her own child the kind of education that her favoured policy would deny everybody else. The Conservative Party put out a board game called Hypocrisy (£19.99) in which one way of earning hypocrisy points was to be a Labour supporter sending one's children to a grammar school.

Harman issued several defences of her decision, appealing to a number of different considerations: I think parents will understand we had to make the right decision for our child and that we would have been less than human if we had done anything else . . . It is simply not right to use your children for political purposes or to advance your political career . . . I believe passionately that you cannot use one child as a piece of social engineering . . . Labour did not create the system in which we are making our choice.

As a political philosopher, trained to separate out arguments that others run together, it struck me that there was scope for some helpful disentangling here. My view was confirmed by the press coverage that followed, as many parents wrote to the newspapers reporting, often in anguished terms, their own attempts to deal with the apparent conflict between their political beliefs and their personal commitments. Here, perhaps, was an area where skills learned in the ivory tower could contribute to a clearer understanding of a subject that exercises real people, not just political philosophers.

It has exercised me for as long as I can remember. When I was 7, in 1968, my family moved across North London from Highbury to Hampstead. I went from a state primary in Gillespie Road (home of the Arsenal's North Bank) to a very different state primary in Hampstead. At Gillespie Road I had been one of very few middle-class children. I remember feeling unusual because I could read, going up to the older classes to show them how to do sums, and getting into fights. At New End, I found myself surrounded by children who were as good at sums and reading as I was. I didn't get into fights. My parents disagreed about such things, but we moved partly because the schools in Hampstead were 'better'. When I was 11, after some agonising (some of it on my part), I was among the minority to move on to William Ellis, an all-boys grammar. Most of my friends went to Hampstead Comprehensive (which is neither in Hampstead nor a comprehensive - how can it be the latter when it coexists with selective and private schools?). Some went private. Some who could have made the same move as me didn't because they or their parents were opposed to selection. Throughout my time at William Ellis I disapproved of its being a grammar school and was delighted when it went comprehensive, while I was in the Sixth Form.

I have two children, aged 12 and 10, both in local state schools. We live in the catchment area of what is generally regarded as a 'good' comprehensive. Hypothetical and inconclusive discussion suggests that their mother and I disagree about the conditions under which we would consider other options, but we are both optimistic that our discussion will remain hypothetical. Friends and colleagues who live in other parts of Oxford, in London, and many other major cities, envy our position. But other friends and colleagues have taken their children out of these schools and sent them private. In their view, these schools are not 'stretching' their kids enough, are 'not teaching them anything', their kids are bored, the schools do not have or foster the kind of discipline they want, or simply do not have the range of extra-curricular facilities - sport, music - available in private schools.

Meanwhile, my work as an academic is on 'community', 'social justice', 'equality of opportunity', 'meritocracy' and 'social mobility'. I know that middle-class children have three to four times as much chance of getting a middle-class job as do working-class children. I know - doesn't everybody? - that much of this has to do with the link between class and education; that the way we organise schooling contributes to the reproduction of social inequality, perpetuating a system of social stratification characterised by unfair inequalities of opportunity. And I think about what it means to act in accordance with one's principles: how one's political views, about how 'the system' ought to be, relate to one's beliefs and actions as an individual, operating in the world as it is, not as one would wish it.

Much political philosophy is concerned with the ideal society: how political and social institutions, including educational institutions, ought to be. Some of this book will indeed be about that. I will try to explain why you should disapprove of private and selective schools, why our society would be better if they did not exist, why you should vote to get rid of them. But knowing what the ideal society looks like doesn't necessarily tell us much about what to do, here and now, in the far from ideal society we actually live in. This is a work of applied political philosophy. It explores an issue that applies to real people living with real dilemmas in the real world.

Some readers like to know not only where books are coming from, but also where they are going to. Since my conclusion will be welcome to many, I'm more than happy to put it up front. I think there are lots of ways in which parents can, without hypocrisy or inconsistency, send their children to schools that they would vote to abolish. So the book is, potentially, good news for anyone agonising over the issue. Even better news: that decision can be the right one to take. It's not simply that they can avoid hypocrisy. (That turns out to be a bit of a red herring.) Parents may actually be justified in sending their children to the kind of school they would prefer not to exist. So parents don't necessarily have to choose between principle and practice. They needn't feel bad about failing to live up to their ideals. Their values may not demand the sacrifice of their children. One can be a good citizen and a good parent.

That's the good news. The bad news is that this leaves plenty of room for hypocrisy or inconsistency, and plenty of room too for parents making bad - morally bad - choices. I'm sure that many are guilty as charged. Whether the accusation sticks depends on the details of the case. You will have to read the book to find out how.

This short book has been a long time in the writing, and I've incurred many debts along the way. I am very grateful to the Fellows of the British Academy for the Research Readership that allowed me to finish it, to those of Nuffield for giving me the ideal environment in which to do so, to those of Balliol for allowing me time away from my normal duties, and to my colleagues in Oxford's Department of Politics and International Relations for taking on the extra burdens caused by my absence. Much of the first draft was written when visiting the Research School of the Social Sciences at the Australian National University (ANU), and much of it discarded when visiting the Political Science Department at the Massachusetts Institute of Technology (MIT). Thanks to both for their generous hospitality.

I have presented papers on school choice at ANU, Harvard, London's Institute of Education, Nottingham, Oxford, Queen's Ontario, Sussex and Wisconsin. Thanks to all who took the trouble to turn up and offer their suggestions and objections, as well as to the many friends and colleagues who have talked or written to me about the issues: David Bakhurst, Brian Barry, Dan Butt, Paula Casal, Matt Cavanagh, Jerry Cohen, Cecile Fabre, Alastair Fernie, Christine Firth, Joey Fishkin, Elizabeth Frazer, Natalie Gold, Sarah Harper, Douglas Hodge, Richard Holton, Kenneth Macdonald, Anne Macpherson, Andrew Mason, Lukas Meyer, David Miller, John Miller, Russ Muirhead, Stephen Mulhall, Glen Newey, Serena Olsaretti, Martin O'Neill, Carey Oppenheim, Terry O'Schaughnessy, Mark Philp, Jean Seaton, Sebastian Secker Walker, Jane Stapleton, Rebecca Surender, Paul Taylor, Steven Warner and Andrew Williams. Harry Brighouse, Matthew Clayton, Christine Sypnowich and Elaine Unterhalter warrant special mention for reading and providing detailed written comments on a full draft. It was Harry who first suggested that what had begun as a journal paper for academics should become a book for parents - his encouragement and advice throughout have been invaluable. Seeing all those names, I'm acutely aware of how lucky I have been, and can only hope that the book shows some sign of the help that I've received in writing it. Since it has undergone such expert scrutiny, any mistakes that remain can be due only to my obstinacy. The book was written in such propitious circumstances that I cannot in honesty offer Danny and Lillie the conventional apologetic gratitude for having put up with an unusually grumpy or absent dad. I can, though, thank them for being a constant joy. It is dedicated, with much love, to my mother, who taught me to agonise.