What is this middle-class panic over school lotteries really about? Does it stem from fear about long-off GCSE results, expecting a place at the league table equivalent of Chelsea but ending up with Crewe? Or is it something more primal and tribal, something never explicitly acknowledged for all its un-PC implications of snobbery and racism: anxiety that our children will not be educated among People Like Us?

It is an impulse that, when given a religious expression, garners unquestioning support from the State. Of course Catholic parents should be allowed to raise children among fellow reciters of the rosary or Muslim parents to choose Islamic faith schools where their properly shrouded girls can be educated free from uppity secular ways.

Yet what if your beliefs are not religious, but amorphous (if heartfelt), encompassing any or all of the following: piano lessons, harvest festivals, emotional continence, the power of books, a bristling at Margaret Hodge for attacking the Proms (though you'd rather put pins in your eyes than go yourself), a repulsion at slutty kiddy clobber, a bossy sense of responsibility for public spaces, an absolute belief in education ... How hard it is to express what being middle-class means, yet how obvious when you see it.

The reason such folk move to the country or suddenly fill church pews or buy houses around a chosen school like wagons encircling to keep out Injuns is not to perpetuate their own privilege per se, but to ensure their type of children constitute a majority and thus their own values remain uppermost. In London, when a state primary school is signalled by the bush telegraph as “up and coming” it may mean the new head is magnificent but more likely it means that Parents Like Us have established base camp. There will be a few other mums with Orla Kiely bags to talk to in the playground. Little Josh is guaranteed playdates with an Oliver and a Fred. And so a tipping point occurs, as aspirational parents rush into Foxtons waving catchment area maps.

In my experience of an inner London primary school, there can be deep respect and goodwill between different ethnic groups and social classes. We smile hellos, chat at the school fair, gladly exchange favours. But deeper interracial or cross-class friendships are rare. Children have a hardwired instinct to seek out those like themselves, a suspicion or at least unease with difference. Yet understanding that disparate folks can coexist is a vital lesson; and children educated wholly in the white prep-school bubble - and with a vile, largely unchallenged tendency to mock poorer kids as “chavs” - are, for all their nice manners and grade 8 piano, in this sense less equipped for adult life.

But the question the lottery idea throws up is: do middle-class parents hog the best schools or are schools best because middle-class parents hog them? The Government assumes the former and demands that the most coveted places are more evenly divvied up. Yet it also counts on lesser schools being improved because middle-class parents are randomly forced on to their rolls. At primary level this task is not so irksome: parents are perpetually in the playground, can agitate for improvement, raise cash for nicer loos, nag a head to raise her game. (Although they also demand teachers give their precious ones a disproportionate amount of energy.) But above all their children helpfully skew a class's number of keen, manageable pupils.

But at secondary level, who feels equal to improving a failing local school? So big and daunting and scary. The odds so stacked, the culture so alien. At one open evening the head boasted how new CCTV cameras had made his school less prone to intrusion by gangs and emphasised that pupils were only permitted one piercing and no tattoos. A bubble of warm feelings about the fab new science block and improving results abruptly popped. Was this induction day at a borstal? You could sense other hopeful, socially minded but aspirational parents scrub it from their list.

Yet it is often said that bright kids with supportive parents thrive anywhere. Don't worry, we're told, they'll be fine. Indeed, professors of education from three British universities, studying 124 middle-class families from London and two other cities with kids at average and below-average comprehensives discovered they mostly achieved brilliant results, a clutch of places at top universities. Teachers leapt to help them to fulfil potential, even devising special courses so they could stay on.

But, blimey, the investment of parental time and energy required. Many were already activists politically committed to state education, more than half became governors, all monitored their children's progress hawkishly. And ironically, although enrolled in melting-pot schools so they would be better socially integrated, these middle-class students clustered together in the top sets, making few friends with poorer peers.

So is that “fine”? Is it OK for your son or daughter, in practice, to have only a tiny pool of potential pals? Maybe they'll get lucky with classmates or stick to their best mate from primary. Blessed with social dexterity they might develop that unteachable, priceless life-skill of getting on with anyone. But what if they are eccentric, bookish, off-the-wall? Will a few years of mockery and bullying knock off their corners, put a little grit in the old oyster? Or will it break their spirits? Fine if they are the kind of easygoing yet focused child who can zone out anti-learning static. But what if they are budding alpha males, magnetised towards the bad boys?

Frankly they all have less cause for sympathy than clever, potentially high-achieving working-class children who lack financial resources and parents confident and wily enough to work the system. A friend of mine, a Jewish grammar school boy from Leeds, is writing a book about social mobility. Where today, he asks, are the stories of local boy/girl made good, the inspiring heroes of Saturday Night and Sunday Morning, Room at the Top, A Taste of Honey, who burst through the limits of their backgrounds? Now all we have is Shameless, rap videos and other nihilistic, ghetto wallowings.

But if the Government believes middle-class parents are useful agents of change, they should address their fears and stop treating them like the enemy. In Brighton, the rush of the disaffected into the private sector is a catastrophe for state schools. And, at root, it has surprisingly little to do with education.

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