Following the announcement that Durham University's only all-women's college is to admit male students, Women's Editor Christen Pears looks at the debate on single-sex education.

WHEN I visited St Mary's in 2002, the college was celebrating its 50th anniversary on its current site. Students past and present had come together to reminisce and wax lyrical about the virtues of an all-female institution.

This was no quasi-nunnery, inhabited by spinster dons and serious, spectacle-wearing students, but a vibrant and thriving community.

Principal Jenny Hobbs told me the college was still relevant to the 21st century and that she did not envisage a future which included male students. But last week, St Mary's bowed to pressure and agreed to allow men through its doors from October 2005.

St Mary's is the last of Durham University's Colleges to go co-ed as part of a national trend that dates back to the 1970s and is bucked only by the students of St Hilda's in Oxford. In December, the feisty females voted for the second time in a year to keep men out. But how long can they hold out?

Since the emergence of feminism, equality has been a keyword on the education agenda. Educationalists wanted to end the underachievement of girls and the stereotyping of subject choices and jobs. The best way to do that was to abandon single-sex schools and colleges and bring boys and girls together in the classroom and lecture room.

St Mary's College traces its origins back to 1899, when it opened as a hostel for six women students in Claypath. Its first principal, Laura Maria Roberts, was a pioneer of women's education both in Durham and Oxford, where she had been one of the first ten students at St Hilda's. St Mary's officially became a college of the university in 1920 and now occupies a superb site on Elvet Hill, overlooking the cathedral.

When I talked to students last year, they told me of its communal spirit and strong tradition of pastoral care, as well as opportunities for leadership and responsibility. Sadly, the number of girls who seem to appreciate these opportunities has dwindled.

The admission of men has been talked about at St Mary's for the last 30 years but, during the 1970s, when other colleges were rushing to go mixed, St Mary's held out. However, during the 1980s, the number of applicants began to fall. Of the 20,000 students who specified a first-choice college this year, only 194 chose St Mary's.

In the past, the decision was left largely to the colleges but changes in structure have given more power to the university and in 1998, a working group was set up to review undergraduate admissions at the college.

Jenny Hobbs was appointed principal in 1999 and began to look at new ways to market the college and make it more pro-active.

"We have worked extremely hard and things have improved, but the university has decided they haven't improved enough. It is a bit sad but we have explored all the possibilities. I think it's an historic moment for St Mary's but we will go forward with a new set of challenges," she says.

The students seem to be embracing the future. All were consulted and kept informed and, of the Junior Common Room (JCR) members who voted on the issue, 60 per cent were in favour of going mixed.

JCR president Hayley O'Connor says: "Obviously it will be an enormous change but I think St Mary's will have a very positive future. It's not like Oxford or Cambridge, where you are taught in college, we already mix with people from other colleges at lectures and in university societies but still manage to keep our own identity. I think that will continue."

When the first male students arrive in 2005, St Mary's will still have women who applied because it was all-female, perhaps for social, cultural or religious reasons. Their needs will continue to be met with single-sex accommodation.

The trend towards mixed institutions is just as pronounced outside higher education. Single-sex schools have almost vanished from the state sector and are gradually disappearing from the independent sector amid arguments that they leave pupils ill-equipped to mix with the opposite sex.

Today, there just over 200 girls' senior schools in the state sector and a similar number of independent ones, while the number of boys' schools is even fewer.

Girls made history at the Royal Grammar School in Newcastle in 2001 when they were admitted for the first time in its 450-year history. At first, only the sixth form was mixed, but last summer, the independent school announced it would open its doors to under-16s in 2006 or 2007.

But a survey published by the Scottish Centre for Research in Education last year said that far from being an anachronism that should be allowed to die out, single-sex schooling has enormous benefits. In some areas, demand is outstripping provision.

Mixed schooling was meant to counter the under-achievement of girls but Lesley Smith, headmistress of Newcastle Church High School, argues that the move hasn't just eliminated the trend but reversed it. Girls are regularly outperforming their male contemporaries in exams. Progress, she says, has been "at the expense of boys' academic achievement".

Phil Garner, head of Ascham House School in Newcastle, has also argued in favour of single-sex education. "Boys' schools give all boys an opportunity to express their talents without feeling inhibited by the presence of girls and unhelpful gender stereotyping," he says.

There are, however, plenty of arguments against. The cloistered, female environment may suit those who are happy to work hard but it can spawn resentment among others, turning them into St Trinian's-style tearaways. Shy girls may benefit in the short-term from having no boys around to dent their confidence but chances are, they'll suffer in the long-term when they make the transition to mixed colleges or universities because they're so unused to interacting with members of the opposite sex.

Perhaps the answer is choice - parental choice and student choice. Single-sex education may be rapidly going out of fashion but it still has a place. The decision of institutions such as St Mary's denies us that choice.