Rachel Mason, headteacher, had a bad day at the end of last term. She was exposed as a former prostitute in front of the whole school and barely had time to dry her tears and touch up her mascara when she discovered that the head of English was trying to cover up an exam board investigation into cheating.

Then an explosion in the canteen caused a fire to spread throughout the school. Rachel steered dozens of children to safety, dealt with a boy having an asthma attack on the stairs, conducted a last sweep of the building only to be knocked unconscious after being hit by falling rubble. A typical day in the life of a headteacher? Perhaps not, but this is no ordinary school - this is Waterloo Road.

The BBC drama, made by Shed Productions, the company responsible for Footballers’ Wives and Bad Girls, has been running since 2006 and this month enters its fourth series.

Ann McManus, Shed Productions’ creative director, is a former teacher from a family of teachers: her mother was a teacher, as was her aunt and her two brothers (one started writing for Waterloo Road 18 months ago, the other is now a lawyer). And Waterloo Road is her pet project. At its peak, Waterloo Road brought in six million viewers, and tackled everything ranging from vocational education as a means of motivating pupils, to violence in schools, leadership issues, immigration and plagiarism.

Its characters are the “integrated architects” of any school, says Ann, and she has met them all. Some of her favourite moments in Waterloo Road have involved Steph Haydock, “crap teacher” and “shagaholic”. But there is a serious theme running behind the drama, humour and campness, she insists, and that is a few good teachers can make a huge difference.

Ann entered teaching passionate about her subject, English. “I really wanted to be a teacher,” she says.

“I thought by being a teacher I’d be able to maintain contact with my subject, English language and literature. I had been affected by good teachers, particularly a couple of good English teachers, so I knew the impact you could have.”

But then Ann got her first job in the Eighties at Grange Secondary, which served Castlemilk, a deprived area of Glasgow. It was a “horrible time” in Scottish education, she says, when schools lacked funding, teacher professionalism was being called into question and staff were striking. Ultimately it proved to be too much. “I’ve never seen such a lack of resources,” she says of Grange Secondary, which has since closed. “The building was so run down and the teachers were jaded. After a few years of Thatcherite Britain, education was horribly under resourced.”

She quickly became disillusioned and in spite of a few good years at Stonelaw High in South Lanarkshire under the leadership of Brian Cooklin, the then department head, now the school’s headteacher and the outgoing president of School Leaders Scotland, Ann beat a hasty retreat.

She started her career in TV as a writer on Take the High Road and in 1998 founded Shed Productions with Brian Park, Eileen Gallagher and Maureen Chadwick.

Brian, Ann’s former department head, remains to be convinced of Waterloo Road’s role as a forum in which to tackle educational issues. He has watched some of the show but never a full episode and describes it as chewing gum for the eyes.

He says Ann was a good teacher but that Waterloo Road is not the kind of persuasive film-making that can shape public opinion. Its purpose is to entertain - it is a soap opera set in a school - and people are as likely to be influenced by it as they are to believe Coronation Street is an accurate portrayal of life in Manchester.

“It’s the TV version of The Sun newspaper,” says Brian. “Nobody is seriously going to say this influences opinion. What it might do is reinforce prejudices in terms of the behaviour that people might believe is typical.” But, he concedes, the programme does not set out to say `this is what all pupils are like’. It’s a piece of entertainment.

Barry Mochan, an English teacher at Dalziel High in North Lanarkshire, used to be a regular viewer and has been told by pupils that he is the spiting image of “the short, fat, bearded” teacher in Waterloo Road - he forgets the character’s name.

Barry says he watched the show not for its realism but mainly for a laugh. “It is simplistic and I don’t think it’s an accurate portrayal of what it’s like to work in a school,” he says.

“All the teachers are stereotypes. One never listens to a word the pupils say; another is like a mother to them; and there’s a young teacher struggling to cope. The issues the programme highlights are just the latest scare stories run in the tabloid press.”

However, Barry does think the show could influence people’s attitudes towards teachers, schools and education. “The first question anybody watching the show who isn’t a teacher asks is: `Is that what it’s really like?’ It is frustrating. I think teachers are more productive and their days are more testing than the picture Waterloo Road presents.”

Patricia Thomson, professor of education at Nottingham University, certainly believes Waterloo Road should not be dismissed out of hand. She feels anything about a school that attracts five million viewers ought to be taken seriously.

“How does the general public find out about what’s going on in schools?” she asks. “A lot of the viewers probably don’t buy The TES or the Education Guardian. This is a point for them to think about what’s going on and find out about it. This programme could help shape people’s views and opinions.”

And Ann isn’t short of opinions herself. Teachers’ basic pay, she argues, should be Pounds 45,000 as it would make a dramatic difference to the quality of candidates in teaching.

She likes uniform, manners in young people and thinks it’s important to set clear boundaries. “We used to have pupils come to school dressed in skinhead gear because they were `expressing their creativity’. Expressing their creativity by buying clothes from a multi-national clothing manufacturer? Absolute nonsense, it just created gangs.”

The story bank for a series such as Waterloo Road is finite, she says. But Ann, a self-confessed lefty, predicts endless hours of drama should the Conservatives come to power.

Meanwhile, this series will highlight the havoc that one chaotic family can reap when, like Waterloo Road, a school decides not to exclude pupils. How schools struggle to cope with the sexualisation of girls, or how they counter the prevailing culture of Playboy pencil cases and FCUK T-shirts, will also be tackled.

But now that Ann is out of the classroom how does she know the real issues facing schools? She reads The TES. Clearly it’s time to take Waterloo Road more seriously.

The new series of Waterloo Road begins on Wednesday, January 7 at 8pm on BBC One.