The drawing of a circle on a map displayed on the wall of headteacher Aydin Onac's office looks anodyne enough but it's what most prospective house-buyers in Muswell Hill are desperate to see. Described from a central compass point that bisects Onac's office, the circle demarcates the precise catchment area of Fortismere calculated to three decimal places. If you buy within its 0.598-mile radius, your children are assured places at Fortismere, one of the top five comprehensives in London, as well as at neighbouring Tetherdown, one of the best 15 primaries in England. But you'll pay up to a 20 per cent premium or £400,000 hard cash for the privilege.

Known as "The Fortismere Factor", it means that a £1.8 million house outside the circle suddenly jumps to £2.2 million when it falls within it, say local estate agents. And although the credit crunch has meant overall prices have fallen by 20 per cent in the past year, the differential remains. Madness, you might say. But actually, insists Onac, it is rooted in sound economics.

"Middle-class parents have calculated that by moving into our catchment area they are getting the equivalent of a private education for nothing. I estimate that a family with two children will save £250,000 in private school fees by sending them to us and Tetherdown, and a family of four £500,000."

School catchment areas and the annual battle by parents to place their children in the school of their choice are becoming more and more divisive as the recession forces increasing numbers of cost-cutting middle-class families to opt out of private education in favour of the best state schools.

Last Friday, on the deadline for September 2009 secondary school admissions, the Evening Standard revealed that one third of families have been rejected by their top-rated school this year. In some boroughs, barely half of children received an offer from their first-choice secondary, while almost 6,000 failed to secure a place at any of their six preferred options.

Onac says: "My heart goes out to those parents and children who have their hearts set on a certain school and who will be bitterly disappointed. The situation families face here at Fortismere is even more competitive as we are one of the 100 most oversubscribed schools in the country.

"I am anticipating that we will have had in excess of 1,200 applications for 243 places, which means that 80 per cent of families who apply will be denied a place. The local authority doesn't tell us how many of the 1,200 who apply put Fortismere as their first choice, but with our outstanding results you can make your own conclusions."

Does Onac think that Haringey Education Authority should follow the radical lead of Ealing, which is talking about doing away with catchment areas entirely? "I am aware of various initiatives by different councils, and although at the moment our school governors are not pursuing that route, we are considering a change to our admissions criteria," he admits. 

"I've got to choose my words carefully here because selecting on the basis of ability is against the rules for a comprehensive, but the admissions code allows us to admit up to 10 per cent of the Year Seven intake based on their aptitude in the school's key specialist subject areas in our case music and languages and we are currently considering that.

"It would be good if some families who live beyond the 0.598-mile radius had a chance of getting their children into Fortismere without having to become millionaires."

Onac welcomes the "long-overdue" Government decision to scrap Sats tests for 14-year-olds. "You don't fatten the pig by constantly weighing it," he says, believing GCSE and A-level results are what schools should be judged on. 

"Last year almost half of our 180 GCSE student-cohort got A*s or As, up from 25 per cent, and almost 60 per cent of our A-level students got A or B grades, the best ever results for Fortismere," he says. "We also had eight students confirm their places at Oxford, Cambridge or medical school, up from just one student the year before."

How do these results compare to the top private schools? "Recently I did a little exercise," Onac says. "I looked at how many students the average private school enters for GCSEs, which was around 100, and I compared them with our top 100 and you know what we knocked spots off most independent and selective schools in Greater London. We were the equal of UCS [University College School] and Highgate School and only a whisker away from Henrietta Barnett, one of the most selective schools in the country."

It is results like these that have put Fortismere on the map. Such is the clamour that some local estate agents are known to keep flats within the catchment which they rent at inflated prices to families seeking to "fiddle the system" by taking out short-term lets during the selection period. Mark Ellis, manager of local estate agent Prickett & Ellis, says: "I often spend more time speaking to prospective buyers about schools than the property they are there to buy."

But despite the rise of Fortismere up the league tables, Onac, who took over the headship two-and-a-half years ago, has proved a controversial appointment. This is because Haringey council, the National Union of Teachers and a vociferous minority group of parents believe his unashamed pursuit of results is to the detriment of the catchment's less academic children. So vehement were they in opposing his vision that he came close, he says, to resigning his £110,000-a-year headship on several occasions.

"When I joined in April 2006, I inherited a school held back by an egalitarian mindset that was stuck in the Seventies," says Onac, 55, who is of mixed English and Turkish descent and lives with his partner, also a teacher, in Hampstead. "I had no idea how deep-set it was, or that I faced the battle of my life to let people know just who was in charge.

"There were moments I thought about whether I really wanted the aggravation, especially when I was approached by headhunters to join other schools on a salary of £140,000. I decided to stay because I'm not a quitter, because I believed I had the support of the silent majority of parents, and because I thought my vision was in the best interests of the children."

Instead, Onac took on the NUT, Haringey council and the disgruntled parents all at once. It came to a head with his battle last year to pursue foundation status, which would take Fortismere out of council control and give the governors power over the school's land, admissions criteria and teachers' salaries.

But a high-profile group of parents which included theatre director David Thacker and Guardian writer Simon Hattenstone set up in opposition. They started a website called Keep Fortismere Comprehensive and held numerous public meetings where they condemned Onac and called for him to be "immediately sacked".

At stake was the soul of a comprehensive regarded as the jewel in the crown in Haringey. More than 70 per cent of Fortismere pupils its most notable alumnus is former X Files actress Gillian Anderson consistently achieved five A*-C grade GCSEs (including English and maths) under previous headteacher Andrew Nixon, who had been there for 23 years. When Onac was headhunted from a state school in Gloucestershire to take over at Fortismere, he was expected to continue in the same vein as his predecessor, valuing inclusiveness and egalitarianism above excellence.

But Onac never read the script. Perhaps they should have seen the signs for Onac thrives on challenge. Before he took a maths degree at University College London and fell into teaching by accident, he was a concert pianist from the Royal College of Music who performed Rachmaninov with the Royal Philharmonic Orchestra at the Royal Albert Hall. The child of an immigrant father, a metallurgist working for British Steel near Sheffield, he had grown up on a tough council estate where the neighbours were factory workers and where he was the only one in his entire school to pass the old 11-plus exam. "I learned that the only way to get ahead in life was to be top," he says.

"My first thought on coming to Fortismere," he adds, "was that given that most families here are wealthy or middle-class (only seven per cent on free school meals), our academic performance was mediocre. Often students had a lackadaisical attitude. This extended to sixth formers who said: 'We're a state school, we can't think of Oxbridge.'

"I arranged for the students to visit Oxford colleges by the busload and this year we got 10 students into Oxbridge and medical school, and half the cohort into Russell Group universities."

But to lift aspirations, Onac had to change the ethos. He began by scrapping mixed-ability classrooms and "setting" the pupils by ability for all subjects. It provoked an uproar from parents who complained that poorly performing children were being "removed and separated" almost like ethnic cleansing and that it compromised "equal opportunities".

Onac counters: "I'm all for equal opportunity, but equal opportunity means realising each child is different and challenging them at their level, not lumping them in one class."

He also set about tackling "lax behaviour" and "lack of respect" the product, he says baldly, of "arrogance bred out of affluence". "Children would put their feet on the desks, talk over teachers and had a sense of entitlement that they owned the classroom. That has changed completely. Now I walk round the school and I see classrooms where it's absolutely clear who is in charge."

But even though Onac won foundation status last year, giving him more control, he is frustrated that the Government does not fund schools directly, as they do academies. "The Government gives £10 million to our school but we only see £9 million of it because the council creams off £1 million for itself. What they do for this money " he rolls his eyes " I don't know, but they seem to employ a lot of consultants. If the Government is saying direct funding of academies is the best way to kickstart a new generation of schools, why not apply this across the board? My message to Gordon Brown is plain: give us the money, we'll deliver the quality.

"Also," he says, "the message from the Government and the LEA is that the worse you are, the more we'll fund you. How can that be right?" He cites a recent £165 million government grant to Haringey schools part of the Building Schools for the Future government initiative as a case in point. "If that money had been split equally between all secondary schools in Haringey, Fortismere would have got £16 million for new buildings, but we only got £4 million because we're not in a deprived area."

In his determination to take Fortismere from "very good" to "excellent", there is nothing he will not contemplate changing, he says. "Except for one thing," he smiles, pointing to pupils dressed in faded jeans and T-shirts. "Some people thought that because I'm a disciplinarian, I'd introduce a school uniform. But the word 'uniform' means 'the same', and I don't want our children to be the same. I don't even care if they wear hoodies. As long as they get what I'm about: that only their best will suffice, and that it's cool to be clever."

• 

  Lenny Henry: 'Maybe one day we can have a black Doctor Who'

  As he wins the outstanding newcomer prize at the Evening Standard theatre awards for his role as Othello, Lenny Henry has come a long way from black and white minstrels

  ---

• 

  Spread of the Jedhead

  Jedward, voted off the X-Factor this weekend, are the most obvious proponents of the sticky-uppy look - but the style crosses boundaries of age, gender, sexuality and taste, says Nick Curtis

  ---

Sky in plot to hire students on the cheap

Sky News is currently recruiting students as reporters for its coverage of next year's general election. However, the opportunity doesn't quite seem so appealing

All stories