Everyone is trying to avoid eye contact with the science teacher in case he makes them answer his question about photosynthesis.

But there are no pupils in the lab. It is the 8.15am staff briefing, which is held three times a week and always begins with a teacher demonstrating a lesson technique.

Today it is the turn of Chris Allmey, head of science, who has handed out numbered cards with words including “water”, “oxygen” and “carbon dioxide” as part of a demonstration of “concept mapping”, an approach in which pupils have to explain links between parts of a process.

The idea that staff briefings here should start with teaching tips would have been risible five years ago. Ditto the free fruit in the staffroom, the interactive whiteboards in every classroom, and the school’s on-site reflexologist.

Back then, the school, in Lambeth, south London, had serious weaknesses, the worst exam results in Britain, and suffered a rapid staff turnover that left classes in the hands of a succession of supply teachers.

Its sprawling concrete site, built in the 1970s, also made it tricky to stop pupils misbehaving, and only a handful of parents picked it as their first choice. Pupils tell horror stories of how students waited at the gates to take their money, while teachers recall finding vomit and excrement by the stairs.

Angelica Wallace, 12, summed up the school’s grimmer days in the first stanza of a poem she has written, called “Memories”: “Back in the days People fighting Children screaming Disobedience.”

The technology college still has one of the most challenging intakes in England. Three-quarters of its students are eligible for free meals, the highest proportion for a London secondary. They also have the lowest average attainment in the capital when they arrive at the school.

About 95 per cent of students are from ethnic minorities, more than half do not speak English as a first language, and a quarter are refugees or asylum-seekers. Yet the school has been described as “wonderful” by Tony Blair, and has been praised by inspectors for its outstanding leadership.

Its new intake this September will be pupils whose parents have made it their first choice, and more than 200 teachers recently applied for a post in its maths department. At an evening for new parents, families are amazed to see the school’s gleaming new pound;20 million building, which stands between the Oval cricket ground and the headquarters of MI6.

Lilian Baylis’s story is not straightforward. For a start, it has been “turned round” at least once before - the last time in 1998 when trouble-shooter Yvonne Bates became head for a year-long secondment.

Ms Bates succeeded in bringing the school out of special measures and lifting staff morale.

But it was not plain sailing after her departure. In 2002, only 6 per cent of pupils gained five A*-C grade GCSEs, and a year later the Conservative politician Oliver Letwin said he would “rather beg on the streets” than send his children there.

When Gary Phillips took over as head in 2001, he was the sixth head at the school in five years.

Determined not to repeat previous mistakes, the energetic head has kept up pressure on staff to innovate and involve more and more outside organisations.

Andrew Comley, deputy head, said: “It’s 100 miles an hour here and always has been. Some staff thought the pressure might come off after we came out out of serious weaknesses, but we’ve got to keep up the momentum.”

The school benefits from being relatively small for a secondary, with only about 600 pupils.

Its location near the centre of London makes it easier to attract outside visitors. A few of the exhausting list of activities in a fortnight at the school included visits to the Globe theatre; work with a professional poet, and a Nike-sponsored day of events for all Year 9 girls presented by female hip-hop and break-dancers and Helen Clayton from England’s women’s rugby team.

A few teachers mutter that there are almost too many activities and say they can make it hard to plan lessons. But they are impressed by their head’s ability to find funding.

“He is terrier-like,” said Nicola West Jones, education director of Business in the Community. “If a business person visits, he will always phone them a year later to find out how they can help next.”

Mr Phillips says the extra-curricular events are crucial. He is putting the finishing touches to a project in which pupils will take over an office in the City this summer to run their own business.

“Some schools have an activity week at the end of term - we have an activity year,” he said. “The aim of this school is to transform the life-chances of the children and we won’t do that with bog-standard lessons.

“If my daughter tells me she wants to be an architect, I’ll buy her architecture magazines, I’ll take her to the Design Museum. But most children here don’t have parents who can do that.”

When he became head, Mr Phillips said his three priorities were to improve behaviour, boost attendance and provide richer-quality learning. He said he knew the importance of clear guidelines for discipline and plentiful pastoral support. His own bad behaviour meant he was sent to a strict “approved school” at the age of 12.

Pupils said they noticed the change when staff began enforcing the behaviour code more strictly. Good behaviour is rewarded with points which can be exchanged for rewards, while those who misbehave get clear warnings before punishments, which include detention.

The school’s new three-level building, constructed through the Private Finance Initiative, has helped to make it easier for teachers to keep an eye on students. A one-way system operates on its corridors and staircases to reduce disruption at break-times.

These changes were combined with a sharper focus on teaching: all five of the advanced skills teachers working in Lambeth are employed by the school.

Mr Phillips has many more plans. He wants to set up a children’s centre and a sixth-form centre on the roof, so he has no intention of departing as swiftly as his predecessors.

“I’m 42 now, so I’d hope to be here another 23 years,” he said. “There isn’t a better job to be had.”

* michael.shaw@tes.co.uk