OPINION: Joan Clanchy on the school marms who have loosened their corsets

It is the annual conference of the Girls' Schools Association this week.

I am the longest-serving member of GSA and this is my 20th conference. When I first attended in 1976, our conference was a one-day affair, largely taken up with debating the increase in subscription. The ladies gathered were perhaps a little in the Margaret Rutherford mould, with magnificent bosoms supported by Clyde-built corseting, serviceable jerseys and tweeds. They were mostly unmarried: the words "vocation" and "dedicated" would be much used in retirement speeches. They were also extremely kind to a newcomer. I remember a kind lady tapping my hand and saying: "Just remember, dear, never say 'yes' to anything in a corridor." I have sat through many courses on management since and have never had more useful advice.

The dispute about the subscription, should it be pounds 25 or pounds 30 per annum, caught the mood of the time. We represented girls' schools and we were cheap. We cut costs all the way round: carbon paper was put to dry overnight; yogurt pots were collected to hold water in the art room; headmistresses answered their own phones during the school secretary's lunch hour.

Change has been fast and radical. I think the watershed came with John Rae's presidential speech to HMC in 1977 when he urged the boys' schools to open their doors to girls - in effect, to rescue girls from girls' schools. His innuendo about the dullness and cheeseparing small-mindedness of girls' schools had just enough truth in it to provide the spur.

The message to headmistresses and their governors was to fight back and to spend. GSA conferences in the Eighties reflected their era: they became residential in big conference hotels; they lasted three days; delegates had outfits; shoulders had pads; secretaries of state attended; more headmistresses were married women with families (one remarkable lady seemed to have a new baby to nurse for every second conference). We were urged to take management training, provide role models and teach our girls to smash glass ceilings.

Girls' schools have fought back successfully, not only through our demonstrated academic superiority, but by developing our own style that is distinctive. During the most painful upheavals of the national curriculum years, GSA had a clear, unbowed line and rejected pointless testing. The framework for inspection for GSA schools lays great emphasis on all the management issues in schools and on aiding them to reappraise and review their procedures. It is an economical system headed by an HMI and is neither cosy nor threatening. The schools are constantly supplied with curricular and management information from their officers and committees to jolt them clear of complacency. We have shown ourselves to be a resilient and adaptable lot.

I write before the opening session of this year's conference so I can only speculate. More short skirts, I should think, and soft, long cardigans in fine wool. I would put some money on a few Georgina von Etzdorf scarves, even if the central heating is too hot. I am wearing last year's skirt and blouse from Mulberry and I hope to tell a new batch about never saying "yes" in a corridor.

The writer is head of North London Collegiate School for Girls.