When socialists argue the case against private schools to conservatives, they flatter the middle classes. For instance, Fiona Millar, the partner of the Prime Minister's former adviser Alastair Campbell and an opponent of private education, argues that if the middle classes put their weight into state schools instead of opting out, they would boost standards.
Ms Millar sees her own circle of friends in politics and the media - ebullient and ambitious Labour voters who nevertheless educate their children privately - and thinks that if these people can influence governments, surely they can turn round schools. Nigel Lawson, the former Tory chancellor and school governor, takes a different view about the benign role of a parent. He studiously avoided all school parents'
evenings, explaining to his daughter Nigella, who was 14 at the time, that this would endear her to teachers.
It is true that the parents who overrun their time at school evenings are courting unpopularity. It is a form of greed that is the downside of parental drive. Parents who are successful professionally are not always considerate to others. It is also hard for them to accept that their own children might not be chief executives in waiting.
The kind of people who run banks or government departments are so geared up to implementation and positive thinking that they rarely question the product itself. I recently overheard an investment banker at an expensive London gym discussing his young son's imperfect walk. He tended to shuffle, rather than pick up his feet. The concerned father had consulted neurologists, psychologists, physiotherapists, homeopathists. The conclusion was that the child simply walked that way. "I'm still thinking of surgery," said the banker.
The belief that everything, especially a child, can be fixed with enough money and expertise is misleading - and in a school environment, disruptive. Teachers have finite time. The pushiest parents are not interested in standards collectively but individually. It is why some may be better off at private schools or hiring private tutors. When schools talk of parental involvement they mean back-up - fund-raising, helping out on stalls. They don't mean back-seat teaching; spying with webcams and smart alec questions intended to humiliate rather than enlighten.
I know an exemplary couple who are zealous about parental intervention.
They write a 1,000-word letter about once a week detailing flaws in teaching or extra-curricular activity at their local comprehensive. Their children crawl into their classroom, mortified. I mentioned them to a supply teacher in case he had come across their campaigns, bust-ups with the local education authority, corrected grammar to the teachers who dared to reply to them. The teacher put his head in his hands. "Everybody has heard of them - they are an utter nightmare," he said.
There is a kind of contract between private schools and parents. If you pay for something, you are entitled to be more of a pain in the arse. State education demands a greater degree of altruism. Ms Millar should be careful what she wishes for.