Jill Berry is having fun. She just did four live radio interviews - one at 6.40am - and she’s knocked out three newspaper articles over the weekend. She doesn’t know whether anyone will publish them yet, but she felt so strongly about the topics that she wrote them anyway.

While Mrs Berry has had a few anxious moments about her new role as president of the Girls’ Schools Association (GSA), the headteacher enjoys being out of her comfort zone and taking risks. “I have always had high self-esteem,” she says. “Some people might say it’s dangerously high.”

Headlines about the evils of celebrity culture, based on a parents’ poll carried out by the association, marked her first week as president. While she doesn’t dissent from her fellow heads’ comments about “low IQ and high heels”, she sees the upside to a world of WAGs and Big Brother. Some aspects of celebrity culture are good, Mrs Berry says. She’s a fan of ER because the American hospital soap and BBC1‘s Casualty may inspire girls to take up medical careers.

Vicky Tuck, her predecessor, spoke about the “toxic cocktail of binge drinking, internet safety and early sexualisation of girls”. Mrs Berry takes a more cheerful view. The association’s survey found that 71 per cent of mothers said it was easier to talk to their daughters than it was for them to talk to their mothers.

“There is less mystique about sex now. My mother never told me the facts of life,” she says. “In Year 6 we have an evening for girls and parents when we talk about sex and relationships.”

If this modern and optimistic view makes the head of Dame Alice Harpur School in Bedford sound different from some hand-wringing politicians and independent school leaders, that’s because she is. “Refreshing is the word” says one of her fellow girls’ school heads.

Mrs Berry grew up in a South Yorkshire village in a family without a tradition of education. Her father was the village bobby and she has two older brothers who are also policemen. When she was 11 she was one of only three children from her primary to be picked for grammar school.

The decision was based on a scheme of continuous assessment, not an 11- plus exam. After a year, the school, Wath-upon-Dearne Grammar School, became a comprehensive. “Independent education was off the radar. I didn’t know where the nearest independent school was,” she says.

Her parents were supportive but had both left school at 13. “I can remember coming home to talk about options. When I raised them with my parents they said: `That’s up to you, luv.’ I felt a bit miffed until I talked to a friend whose father was a professor of maths who had the opposite problem. I wasn’t pressured.”

Mrs Berry knew she wanted to teach. “I was quite bossy. I played games at school in which I was the teacher. Mainly I became a teacher because I wanted to use my subject.” She thought about going to a college of higher education, but the A-level teacher who helped to inspire her love of English told her she should aim higher. She was one of a handful of pupils called to a meeting by the deputy head who said they might be capable of winning a place at Oxbridge, though the school could not give them the support that others provided.

“It sounded pretty discouraging. None of us even considered it. I had the uninformed prejudice that it would be full of posh people and I wouldn’t fit in. When I became a head of English preparing people for Oxbridge I thought that I would probably have loved it.” She went to the University of Manchester.

Though Mrs Berry wanted to be a teacher, she never intended to be a head. “When I was a young teacher, the head was a rather remote figure, busy, stressed and out of touch with staff and pupils. I used to think there was something silly about senior management, particularly the way they danced at the Christmas party.

Yet Mrs Berry was clearly ambitious. At 29, after teaching at Range High School, a comprehensive in Formby on Merseyside, and a job at Wirral Grammar School for Boys, she applied for department head jobs, and was getting increasingly frustrated at being turned down when she became head of English at Altrincham Grammar School for Girls.

She taught there for five years before getting her first job in an independent school. The choice of sector was not deliberate: she had just been turned down for a state school job she really wanted, then went for an interview for deputy head at the independent Nottingham Girls’ High School.

The candidates had to write about the issues facing the independent sector. It was 1994 and Labour’s plan to abolish the assisted places scheme for pupils who could not afford to pay private school fees was on the table. The other candidates wrote about that. She wrote about how crucial it was for independent schools to keep up with a rejuvenated state sector that had Ofsted, the national curriculum and tests.

Five years later she was appointed to her present post as head of Dame Alice Harpur School. Mrs Berry thinks all heads would benefit from a stint in independent and state schools. “I’m a better head because I’ve been in different schools,” she says. “It gives you a bigger picture.”

Mrs Berry’s relationship with her pupils is at the heart of what she does. Some of her staff, she says, think that she is not hard enough on the girls.

Fellow heads see this as lightness of touch. One says: “I imagine they very much want to do the right thing for her because they want her good opinion.”

She teaches every Year 7 pupil. The highs and lows of her career involve pupils. Her favourite moments include singing in the choir with them and flying a two-seater aeroplane when those in the RAF section of the Combined Cadet Force were doing their training; her worst, the death of a pupil, or saying goodbye to someone whose parents can no longer afford the fees.

Mrs Berry is 50 and has written a diary since 1973. She is reading the entries for 30 years ago to remind herself of her own teenage angst. Every year she wrote new year resolutions in the back. In 1975, when she was 16, there were 50. One was: “Always to concentrate in class even if it’s boring”. This year she will use the diary resolutions as the topic for an assembly. Of course, she’ll say with a twinkle in her eye that their lessons are never boring.

She works a six-day week and can work an 80-hour one if necessary. When she became a head she decided that she would read every comment on every pupil’s report: that’s for 850 girls, sometimes twice a year. “The only way I can do it is by working until midnight several nights a week.”

Mrs Berry lives in Bedford in the week and then goes home to Newark and her husband. He is a research scientist, consultant and lay Ofsted inspector so is often travelling. Her lifestyle is easier, perhaps, because she has no children. “I would have liked a family, but it just didn’t happen.”

Despite the long hours, Mrs Berry says she is good at organising her work- life balance. Her idea of heaven is relaxing in the sun with a good book. They often holiday abroad, preferably in places they haven’t visited before.

Her role as GSA president adds another layer to her workload, but Mrs Berry relishes the prospect. Her commitment to single-sex education is total. “If you educate the sexes separately you bring out the best in both. My first experience of a girls’ school took me by surprise. They were more confident, less self-conscious than they were in a co-ed school. In a co-ed school, girls are so much more aware of what others, particularly boys, think of them.”

But isn’t this image of the retiring girl cowed into silence by her boisterous male classmates out of date? Haven’t the academic advances made by girls during the past 30 years laid that notion to rest? “I don’t have this great sense that the world has moved on. At particular ages, girls are as self-conscious as ever. Girls who have been to co-ed primary schools tell us that boys take teachers’ time.”

Mrs Berry has admirers in the Headmasters’ and Headmistresses’ Conference (HMC), the parallel organisation for leading boys and co-educational schools.

“She is extremely bright and enthusiastic,” says one member.

But she is unlikely to give much quarter to those who are hoping for a truce in the long-standing debate about the merits of single-sex education. A report by Professor Alan Smithers, commissioned by the HMC, said that there was no evidence that girls did better academically or socially in single-sex schools. The report said girls’ schools were successful because they were so selective.

Mrs Berry dismisses this: “I know what outcome HMC wanted for that research. Not all GSA schools are highly selective. This isn’t about specific research - it’s about 30 years’ experience in different types of school.”

She doesn’t argue that single-sex schools are the most important factor in academic success: good teachers, leadership and organisation are obviously more important. However, Mrs Berry does believe that teaching has to recognise clear differences between the sexes. You only have to look at the way boys and girls play. “If a girl wants to play a game and her friends don’t, she will find another game. A boy who wants to play cricket will ask his friends to play. If they won’t he will go and ask someone else to play cricket,” she says.

Her decision to leave teaching next year, shortly after her presidential year finishes, has raised a few eyebrows. Her fellow heads comment on her youthful demeanour. But she will have completed 30 years in the profession and says she is looking forward to some different, though education- related, work, perhaps involving inspection, where she has plenty of experience, and headteacher appraisals.

No one who encounters Mrs Berry could suppose that she is retreating disillusioned or defeated. “Education is getting better. We know so much more about how the brain works. We know more about engaging pupils.”

Mrs Berry also believes that this Government has been more supportive of independent schools “than any previous regime”, and she is keen on independent-state school partnerships. As for her job: “The head’s is the best job in school. Every day when I walk into school I feel positive.”