Mari Williams has got used to being called barmy. “When I tell people I teach,” says Mari, “they ask, ‘What age?’, and I say, ‘11 to 16’. Then they go, ‘Oh, wow, that must be tough,’ and you can see they’re thinking, ‘Why is she doing that?’ Then they ask where. When I say, ‘East Ham’, their jaws drop. They think I’m mad.”

But Ms Williams isn’t mad, just committed - committed to teaching and to the large comprehensive in the London borough of Newham, where she is halfway through her first year as a history teacher. With 2,000 pupils, Langdon is one of the largest 11-16 schools in Britain. Considering Newham’s inclusive educational policy and the area’s diverse social and ethnic mix, it could be considered a challenge for your first teaching job.

But for Ms Williams, it feels like the real world again. After two years in public relations, she decided to become a teacher, because she didn’t want to spend her life “doing something peripheral”. She says:“I was swanning around in a middle-class bubble. I wanted to do a real job, one that matters.”

And what matters to her, she says, can be traced back to her own education in a similarly large, mixed comprehensive in Cardiff. Ms Williams comes from the Rhiwbina area of the Welsh capital and went to Whitchurch high school from 1987 to 1994. “Going to a comprehensive myself had a massive influence,” she says. “It gives you an appreciation of the real world, and a realistic perspective on life.”

Ms Williams, along with the Manchester United footballers Phil and Gary Neville (who both went to Elton high school, Bury) and author Zadie Smith (who went to Hampstead school in north London), has put her name to the Comprehensive Champions campaign, launched last month by the Campaign for State Education (Case) to counter the damaged public image of comprehensives.

“Comprehensives have become tarnished by the ‘bog-standard’ tag,” says Margaret Tulloch of Case. “You hear people say, ‘Oh, I only went to a comprehensive’, as if it’s a stigma. We want to highlight the voices of people who value having been to comprehensive schools.”

The campaign is partly a reaction to what Case sees as a drift away from the comprehensive ideal that revolutionised secondary education in the Sixties and Seventies. Of the 3,500 state secondaries in England today, only 164 are grammar schools, but the campaign’s supporters see the growth of specialist and faith schools as a mistake.

They point to comprehensives’ academic record: in 1965, when only 8 per cent of secondary pupils were in comprehensive schools, 17 per cent of school-leavers had five passes at O-level or grade 1 CSE, whereas in 2000, when almost 87 per cent were taught in comprehensives, almost one in two achieved five A*-C GCSEs. These figures, they say, show how the shift to mixed-ability education has “levelled up” standards.

MEP Glenys Kinnock went to one of Britain’s first comprehensive schools, Holyhead, in north Wales, in 1955. She probably wouldn’t have passed the 11-plus, she says. “I wasn’t a model pupil. I talked a lot and was bad at maths. Temperamentally, I wasn’t ready to settle down and make that kind of effort at 11.”

But at Holyhead, Ms Kinnock “surprised everyone” by getting a string of good O-levels. She was made head girl, “in recognition of this transformation”, went on to take A-levels, and headed off to Cardiff University, where she trained to be a teacher. “I always enjoyed school and always wanted to teach,” she says.

But academic achievement is only part of the comprehensive equation. Professor Geoff Whitty, director of London University’s Institute of Education, wrote a paper last year, Has Comprehensive Education a Future under New Labour?, in which he said: “Comprehensive schools are even more important to the social inclusion agenda than to the standards agenda.” He and others argue that it’s the experience of mixed-ability, mixed-background schooling that has most significantly shaped and identified the comprehensive generations.

Amanda Stevenson also went to a large comprehensive, in Durham during the Seventies and early Eighties, and she, too, is keenly aware of the opportunities it gave her. “I saw kids at school who had a much harder upbringing than me, but I also met people who were more middle-class and had greater expectations. I had no academic background and it helped me see what was possible.” Now head of English at a large inner-city comprehensive in Leeds, she says she became a teacher partly as a way of “putting something back”.

That sense of having encountered a broader spectrum of human life than would otherwise have been possible is one of Gillian Drinkwater’s clearest memories of secondary school. She went to Sir William Romney’s school in Tetbury, Gloucestershire, shortly after it went comprehensive in the early Seventies. “I remember I used to walk to school through a huge council estate,” she says. “My best friend came from that estate. I’d never have met her if it had still been a grammar.”

Ms Drinkwater has been teaching at primary schools in east London for more than 15 years now, and although the area’s social and cultural mix could hardly be more different from that of Gloucestershire, she still believes her school experiences have helped her handle, and appreciate, the job. “Comprehensive school gave me an idea about what the world is like for most people,” she says. “When I came across people who had been to selective or single-sex schools I’d think they hadn’t got a clue about the real world.”

Flora Page went to Islington Green school in London between 1983 and 1988. It, too, bordered a large housing estate, and Ms Page - now a criminal lawyer - says that, although she remembers being bullied, she valued the rough and tumble of the comprehensive mix.

“I was aware that it was good experience,” she says. “And I was pleased not to be surrounded by people like me.” Even the bad stuff has stood her in good stead professionally. “Many of my clients are poorly educated,” she says. “And many other criminal lawyers don’t know how to communicate with them. I’d find my job much more difficult if I didn’t have a broader awareness of life.”

The ability to communicate effectively with a wide variety of people is something Mark Johnson also values from his schooldays. Mr Johnson went to Framwellgate Moor comprehensive in Durham before training to be a doctor. He now works at a large hospital in Newcastle upon Tyne. “Medicine is full of doctor’s children, many of them privately educated,” he says. “A lot of medicine is about dealing with a broad range of people and I certainly think I’m more capable of that than some of my posher colleagues. Some don’t seem to have a clue what’s going on sometimes. Some of the older doctors in particular seem unable to interact with the rough diamonds.”

Of course, he says, it’s not only school that gives you that - “a lot comes from family and the way you’re brought up”. And, he adds hastily: “Many people who’ve been to public or selective schools become good doctors.”

Many become good teachers, too. Although maybe not at Mari Williams’s school, where even she is considered posh. “My pupils think it’s hilarious that I don’t understand their huge range of language,” she laughs. “I can still relate to them though. I want to widen the children’s horizons, to help them see there’s a world beyond East Ham. The most important thing is that they come out with a decent education and can move on.”

And maybe, one day, they’ll become comprehensive champions, too.

To contact Case, tel 020 8944 8206; www.casenet.org.ukchampionsCentre for Supporting Comprehensive Schooling: 01604 492 337; www.mplc.co.ukorgscscsFurther reading: Affirming the Comprehensive Ideal, edited by Richard Pring and Geoffrey Walford (RoutledgeFalmer pound;17.99). Promoting Comprehensive Education in the 21st Century, edited by Clyde Chitty and Brian Simon (Trentham Books pound;13.95)

STORY OF THE COMP

* Late 1950s A handful of local authorities set up ‘experimental’

comprehensive schools. The move is prompted by concerns that psychometric testing techniques are flawed

* 1965 New Labour government asks LEAs to move towards the comprehensive model. Authorities such as Anglesey, Bradford, Croydon and Leicestershire lead the way in implementing the new policy

* 1976 An attempt to force LEAs to adopt the comprehensive model is ruled unlawful

* 1988 Education Act introduces grant-maintained status, paving way for reintroduction of selection in previously comprehensive authorities

* In 1965 8 per cent of secondary pupils went to comprehensives, and 17 per cent got five passes at GCSE equivalent (O-level or grade 1 CSE); in 1998 nearly 87 per cent were in comprehensives, and 46 per cent got five or more GCSE passes at grades A*-C

* In 1970 47 per cent left school with no graded exam results; in 2000 the figure was 5.4 per cent

* Between 1989 and 1999 the proportion of 16 to 18-year-olds in full-time education rose from 38 to 75 per cent

* In 1971-72 14 per cent of under-21s entered higher education; by 1999-2000 the figure had risen to 32 per cent

* There are still 164 grammar schools, found in 25 per cent of English LEAs (36). There are 15 LEAs in which about 20 per cent of children go to grammar schools Source: Comprehensive Secondary Education: Building on Success. Available on the Case website at www.casenet.org.uksuccess.html