First Essex and Yorkshire, now London: Channel 4's 'Educating...' series is moving to the East End

The show is turning its cameras on Frederick Bremer School in Walthamstow. Simon Usborne goes behind-the-scenes to watch the latest series being filmed

Inside the gallery at Frederick Bremer School in Walthamstow (Frantzesco Kangaris)

At the end of morning break inside Frederick Bremer School, a scene is unfolding that will definitely not make the cut of Educating the East End. Jenny Smith, the very hands-on head teacher, is standing near the main entrance, talking to me, a photographer, the series’ director and someone from Channel 4. Like a police chief on a drugs bust, she juggles the tools and spoils of her trade: a cup of tomato soup and a pair of size 10 Nike trainers.

"I've just confiscated them off Basil," she says after a warm hello and a nod. "Now he's going to have to come to my office and grovel for their return for his PE lesson this afternoon."

It's late April and exams season is gathering pace. Smith is in total command of "the street", a long atrium of glass that forms the heart of her school in Walthamstow. But she's also a little nervous, and not just because we are being watched by several cameras that have been bolted to the walls for seven weeks now; she's also wary after agreeing to allow a journalist to watch the making of an Educating... series for the first time.

"It's really hard holding a mirror up to yourself and having a really good look," she says.

To be precise, Smith has allowed 76 mirrors, or remote-controlled cameras, into her school, as well as 94 microphones and a fleet-footed crew of producers and runners. On Thursday, she and some of her staff and 900 pupils will become the stars of the third series of Educating.... As pupils everywhere prepare to go back to school, those at Frederick Bremer have big shoes to fill: the second series, filmed in Yorkshire, captured awards, viral success and almost three million hearts last year with the story of stammer-defeating Musharaf, or 'Mushy'.

"We won't have a Mushy moment, unless I find a cure for autism in the next two days," Smith says. "But there will be tears – mainly mine."

Smith, more than anyone else at Frederick Bremer, has opened up her own life to the harsh scrutiny of the cameras. "I'm miked up all the time," she adds, glancing down at the device clipped to the neck of her blue dress. "It's like being in The Truman Show."

In the film, an airy operations room is equal parts Bond villain's lair and Nasa mission control. At Frederick Bremer, a windowless shipping container plonked behind the science block does the job. Jo Hughes and Liz Hazell are in charge. They lead the way up the steps to the grey box in the car park, and open a door to reveal a startling sight: more than a dozen people perched, shoulder-to-shoulder, in a cramped, dark space that buzzes with electricity and wired brains. They have been here for seven weeks.

Along one wall, a gallery of screens show what each camera is seeing. In the container below us, engineers manage hard drives as they store hundreds of hours of high-definition footage, from which just eight episodes will later be cut. Cameras 60, 61 and 62 are installed in Smith's office, where she can now be seen at her computer. One shows the whole room, while another is zoomed in on the head's face. I point out quietly that she appears almost to be attending to a nostril. "Let's ignore that," Hughes whispers back.

Three large screens at the centre of the gallery are labelled A, B and C – the video feeds Hughes and co-director Hazell have the capacity to manage and record. Everything else disappears as soon as it has been captured. The enormous technical and editorial challenge becomes deciding which scenes to go with, while also making sure the people in them are equipped with a radio microphone like Smith's (there are 24 clip-on microphones in total: Smith is one of four 'characters' to wear one constantly).

Mr Bispham with students Tawny, Alexandra and Ruth (Frantzesco Kangaris)

In short, the bleary-eyed team have effectively to direct what is happening as if this were a live show. But, unlike The Truman Show, they have no control over what unfolds (nor any malicious intent). They must still capture enough drama in real life – "the extraordinary in the ordinary" as Hughes puts it – to make six and a bit hours of television. The degree to which they have become immersed in the architecture and workings of the school, their equipment, and each other is captivating.

"You start calling camera numbers in your head," says Hughes, who later tells me she's 34, before realising she had turned 35 during filming without having time to realise it. "I know 15 will always be the stairs," she adds. "Fourteen is a key corridor, 75 a science corridor..."

She breaks off and raises her voice. "We still got ears on Palombo?" The assistant head can't be seen on any screen. "He's in his office," Demi Doyle responds. When people are off camera, hearing them via their microphones, or the dozens of fixed mikes around the school, can help the gallery keep track of them. Doyle's job is to listen to all audio feeds, eavesdropping on daily life and alerting the team to action that could be thrown from the small screens on to the big ones.

Later, Doyle hears Mr Bispham, a young new English teacher who has quit a life in politics, dealing with his rowdy year nine class. His struggle to work, in particular with the girls, will later become a key storyline in episode one. Their lives, meanwhile, will reflect the lot of today's teenagers in a London school such as this one. The irrepressible Tawny is desperate to win a place at drama school, and less engaged in Mr Bispham's Shakespeare lessons. When Acacia gets into trouble for sharing an illicit photo on Facebook in a revenge posting, it emerges her mother is desperately ill. Acacia's story has the potential to move millions, but only if it can be captured in the box in the car park.

Hazell, who is standing alongside Hughes, immediately calls for Ben Hoffman, the gallery director, to go with cameras 56 and 57, in Bispham's class, on A and B. It's then the job of Tom Parr, who sits next to Hoffman, to control them. With the dexterity of a Korean teenager on an arcade machine, he punches a camera number into a keypad and, using his other hand, manipulates a joystick to move it. A lever allows him to adjust the zoom; a wheel changes focus. On this occasion, the drama in English subsides, and the directors' exhaustive search for intrigue continues elsewhere.

Planning and organisation is as crucial as responding to events. Hughes pulls out a dog-eared copy of the crew's version of today's school timetable. "So we know Palombo was meant to be mentoring Paris, who turned up late so it didn't happen," she says, tracing a finger over the spreadsheet. "And this is Mr Bennet's form, and these are the students we're looking for in his class. We know Palombo then has business class, and we'll have Mr Mackenzie in that room. This is Bispham now, then Miss Higgins..."

To help further, wedged in the corner of the room, Billy Hussein and Emma Wellbelove are furiously typing brief descriptions of what is happening in the three feeds, two of which tend to be used to capture the same scene. Their vast log, which automatically links to the footage it describes, will later be mined during the edit to help locate clips and organise stories.

One of the 76 remote-controlled cameras mounted throughout the school (Frantzesco Kangaris)

Preparation begins as soon as a school is selected, months before a camera rolls. When Educating Essex was broadcast in late 2011, producers from Twofour, the company behind the programme, approached about 20 schools. Nearly all head teachers said no. The rigged-camera show was then still synonymous with Big Brother, which had become as manipulative as The Truman Show but without any of its brains. Despite early fears that a school might receive similar treatment, Passmores Academy in Harlow eventually said yes.

Educating Essex became a critical and popular success as it emerged that this was something new – a sympathetic series that used technology to realise the dramatic potential in everyday school life. The voyeurism was only compelling because it was honest. Two years later, schools lined up to appear in the second series, and Thornhill Academy in Dewsbury became the setting for Educating Yorkshire. It, too, was funny, moving and – above all – positive about young people. "We talk a lot about teenagers but how often do we ask them what they think and feel?" Hughes asks.

Producers spoke to more than 100 eager schools for series three, and visited more than 40, looking for striving state schools with character and characters. When Frederick Bremer got the nod, Smith says she took calls from both former starring head teachers. "I was thinking, what on Earth have I done? But they told me what an amazing experience it was and how much the school gained. That's what convinced me this was an opportunity we couldn't turn down." The exposure is still daunting, she admits: "One of the things about teaching is that everyone has an opinion about how it could be done better".

Hughes and her team go to great lengths behind the scenes to reassure the school and parents of their intentions. They begin with dozens of meetings and assemblies, and remain engaged throughout and after filming, later sharing footage before broadcast and discussing the potential pitfalls of a life suddenly screened. Those few who prefer not to participate are left out of filming or their faces blurred. "Trust is so important because we're coming into their school," Hughes says, adding: "the absolute priority is that we don't interrupt learning".

Educating... now sets the standard for a family of rigged documentaries that are the noble legacy of Big Brother: One Born Every Minute, The Family, and 24 Hours in A&E, which have also won big audiences and awards. Hughes adds later in an email: "I forget sometimes that people expect us telly people are all the same and will be always seeking out the 'juicy bits' with no regard for the people involved. The reality is the opposite... we care deeply about reflecting [characters] as the often brilliant, brave, funny and articulate people they are."

Outside the claustrophobic container-gallery, where Tom Parr now needs a third hand to control his paper plate of pasta, a ninja army of runners and assistants works quietly in the background. Hughes is now getting them ready for lunch break, typically a frantic time for the team. Crucially, they need to be sure the characters Hughes wants to follow have mikes, updating each device's whereabouts on an iPad using a tracking system invented by Ollie Waton, one of the sound engineers in the gallery.

The school's head teacher, Jenny Smith (Frantzesco Kangaris)

"We definitely want Ida, Gaby and Jordan on," Hughes tells the ground crew via her headset, a permanent fixture. "Can we try leaving on Joshua and Christopher. Is Christopher going to have lunch with Joshua? I could really do with that. Can someone have a chat with him?"

Joshua is in the race to become head boy, a campaign and election that will become another big storyline. Christopher is a student who receives learning support, a constituency Joshua is keen to attract. "They have a really sweet friendship and often talk over lunch, but not yet on film or microphone," Hughes explains. "A lot of this is about capturing the things you know happen all the time anyway."

Sometimes, good things slip through the cracks. "Last night at parents' evening, Jenny had a lovely conversation with one of our characters and her mum about confidence and how to grow it, and we just didn't have the shots," Hughes says. "When you're missing people being brilliant you're gutted because you feel like you're letting them down."

I leave the gallery, breathe in some spring Walthamstow air, and head back into the school as the bell sounds for lunch. I've been instructed to keep a low profile; students won't have to deal with press until shortly before transmission. A mural in the lobby shows the word 'Welcome' in the 60-odd mother tongues represented in the school, which only opened in 2009 in one of London's most diverse and deprived areas. Its motto: 'Aspire, Believe, Create'.

Vanessa Singh and Gagan Rehill are standing by near the playground. They have spent seven weeks embedded in the corridors, building up a rapport with students, many of whom they got to know before filming had begun. "Whenever I'm stressed I have this recurring dream where I'm back at school and the exams are coming and I've got teachers chasing me around and then I wake up," Rehill, aged 30, says. "Now I feel like I'm reliving that moment daily, with a different kind of stress. But it makes me very nostalgic."

"They call us 'Sir' and 'Miss'," adds Singh, an assistant producer. She has been directed by Hughes to meet Anwar as he comes out to lunch. The aspiring street magician is a regular breaktime performer but Hughes needs decent footage. "I'm going to pick him up and ask him what he's up to and if he says he's going to do some magic then great, I can mike him up and tell the gallery there's potential," Singh says. Sure enough, Anwar's up for it and in a very rare occurrence – perhaps the only one during filming, Hughes says – two camera operators are deployed to the playground, where rigged coverage is limited. A crowd quickly gathers as Anwar performs his tricks.

Frederick Bremer School pupils Acacia and Tawny (Frantzesco Kangaris)

Even with tripods and grown men behind cameras in the playground, students appear oblivious to the attention. It brings to mind the question asked by any viewer of this kind of TV: how much are the people we watch playing up to the flies on the walls?

"You go into it thinking, yeah, I'm going to be giving these big speeches and drop all these soundbites," Smith says. "But you forget so quickly that the cameras are there, you really do. This job doesn't leave time for you to be conscious of what you're doing for an audience." The only sign something had changed among teachers, she adds, was a sudden, brief smartening-up of their wardrobes.

More surprisingly, the same appears to apply to students, some of whose behaviour and protestation of innocence in previous series have suggested that they, too, lose awareness of the cameras. "We did a lot of work with them before so they knew that any playing up just wouldn't get featured," Smith says. "They were excited in the first couple of days but if anything it had almost a subconscious, regulating impact because they wanted to be portrayed in the best light. But then they also just forget."

Several weeks later, in late June, I meet Hughes again at a TV studios in Soho. She sits in one of eight editing suites Twofour has block-booked, each of them occupied by two people – for three long months. The task would make any brain hurt: to turn 1,500 hours of footage shot over eight weeks, enough to play constantly for two months, into eight, 47-minute episodes.

Next to her is Martin Thompson, an in-demand editor whom Hughes recruited months ago. Their desk is strewn with paper and sushi boxes. "Filming is immediate because you're on it every minute, making decisions that we now live and die by," Hughes says. "But this is just a stupidly busy time. It's ridiculous how long it takes."

Channel 4 production staff walk out of the temporary gallery (Frantzesco Kangaris)

Each suite is given an episode to work on, while Hughes and Hazell also oversee the series, often switching storylines and characters between programmes right up until transmission. As well as the three recorded feeds from the rig, they draw on a further 100 or more hours of interviews, almost all of them conducted during the shoot in a temporary studio in the car park.

But it's the candid footage that elevates Educating.... "It gives you a view on people's worlds that you could never normally capture," Thompson says. Episode one will include a two-second look shared between Acacia and her sick mother during a parents' evening that is so rich with feeling, Hughes says, it still makes her cry after dozens of viewings. "There's also something about the everydayness that the rig captures," she adds. "Those funny, banal moments that are special and say so much about the human experience."

A folder-full of these 'interstitials' can be used to break up the drama, helping to build the character of the school and pace the films. "They've got a lovely one next door," Hughes says. "It's just girls borrowing hairspray off a boy doing their hair – a moment that isn't editorially significant but makes you think, I remember what school was like."

Otherwise, the standard rules of narrative filmmaking apply, each episode drip-feeding the audience information about the characters involved. As the last few weeks of editing still lies ahead, is there a story to rival Mushy's struggle with his stammer? "Well, no one learns to speak, but I hope very much that people will love these students as much as we do," says Hughes, who plans to watch the series nervously at home, monitoring reactions on Twitter. "I think people have a lot of assumptions about London schools and I hope that while watching this they will change their minds a bit."

It's a hope shared by Smith, who I call after filming has finished, in the middle of exams season. "It's a mixture now of nerves and excitement," she says. "But I've no doubt it will be a very real and raw portrayal of what life is like here. I think it will also have a catalyst effect on us because it will show how hard we all work. It's very easy when you're judged as a struggling school to feel despondent. This is an opportunity to reaffirm our faith in what we do".

'Educating the East End' starts this Thursday at 9pm on Channel 4