The bell sounds for the end of a drizzly lunch break at Gascoigne Primary School. Troops of children, all anoraks and smiling faces, line up to make their way back inside under the watchful eyes of their teachers. It is 1.20pm and lunch started nearly two hours ago.
Headteacher Bob Garton and his senior staff have been on near-constant playtime duty since first break at 10.25am, three hours ago. The endless parade of pupils, shuffling from break time to class, from lessons to lunch, is punctuated only by assembly. At Gascoigne, there are three or four a day.
This is just an average Wednesday in the 1,100-strong primary school in Barking, East London, one of the capital's most deprived areas. What has made things a little more trying is the rain. How a primary with more than a thousand pupils copes with wet playtime is little more than a wonder. Home time is particularly extraordinary. Many hundreds of parents and carers arrive to pick up 1,100 children. To say it's like a military exercise would not do it justice.
"It is challenging," Garton says, half smiling. "But we all know what our jobs are and we manage."
Gascoigne's headteacher has a welcoming, laid-back manner, and he needs it. His school and staff are calm, belying the fact that Gascoigne is bigger than many secondaries, and easily treble the size of some primaries.
A primary school of its size comes with its unique challenges. Christmas-time, for instance, is particularly fraught.
"There was a time when we were doing 12 nativity plays each year," Garton says. "We have 150 pupils in each year, so there was no way we could do one nativity per year group. The parents want to come and we just don't have the space in our hall."
The school has now managed to work around the issue, he adds, but it still means two weeks' worth of the birth of Jesus.
But far from being in a league of its own, Gascoigne Primary could well be a sign of things to come, certainly in areas such as Barking and Dagenham. According to official pupil projections from the Department for Education (DfE), England will need an extra 450,000 primary places by 2015 owing to a surge in birth rates in certain parts of the country.
London alone is in need of 80,000 extra seats, the vast majority of which are within the primary sector. But outside the capital, particularly in areas such as Bristol and Bedford, there is a desperate need for more school places, too.
The shortage has been slowly building over the years like the quiet drip, drip, dripping of a leaking tap. A failure by the previous Labour government to address the problem has meant that the swell in numbers could lead to a flood of pupils entering the system in three years' time without adequate space and resources to cope with them.
The cancellation of the school rebuilding programme, Building Schools for the Future (BSF), coupled with the drastic 60 per cent cut to the DfE's capital budget, has left many onlookers wondering how education secretary Michael Gove intends to meet the demand. Indeed, many suspect that there isn't really a plan. Already the word "crisis" is being whispered around the corridors of Whitehall.
In his Autumn Statement, chancellor George Osborne pledged to give #163;4 billion over the next four years to meet the need in the areas facing the greatest pressure on places. The money equates to #163;800 million a year, with an additional #163;500 million in 2011-12, an extra #163;600 million in 2012-13 and a further #163;600 million for free schools. But already many council bosses, particularly in London, are clamouring that the money will not be enough.
Barking and Dagenham is perhaps the area of most acute need. The borough has seen a huge increase in the number of young families in recent years, and it is expecting to see a 40 per cent rise in primary pupil numbers by 2015. According to the council, by 2020 more than a third of the borough's population will be under the age of 19.
Rocky Gill, cabinet member for education in Barking and Dagenham, says his borough has seen the largest rise in birth rates in London, and probably the UK, up 58 per cent from levels in 2000. Couple this with the government's changes to housing benefit, and the region has seen a massive demographic change as more families come to the area looking for cheaper housing.
The pressure this is exerting on schools, Gill says, has made placing pupils an incredibly difficult task, as the borough is expecting to see the number of primary-age children rocket from 19,000 to 27,000 by 2015.
To try to resolve the problem, Barking and Dagenham has been putting forward some rather unconventional proposals to try to find desks for its extra pupils. One of the more extraordinary plans is to introduce shifts to schools. One cohort of Reception to Year 6 would attend school from 8am to 2pm, and another would come in from 2pm until 7pm.
Such suggestions illustrate the desperation being felt in many town halls, which, having lost out on BSF cash 18 months ago, have not only run out of money but also ideas.
"The current situation is very difficult," Gill says. "To meet this demand, we need to build the equivalent of two four-form-entry primary schools per year. Educationally, we would prefer to be creating three-form-entry primary schools, but in fact five-form-entry schools are the norm in this borough. We even have a number of seven-form-entry schools."
Gascoigne Primary sits squeezed in among Barking's cheap housing, much of it the crumbling stock of the 1960s. Itself a five-form-entry school, it has been at what Garton describes as the "epicentre" of the demographic change in the borough. Only 15 years ago, just 10 per cent of Gascoigne's pupils spoke English as an additional language. Today the ratio has reversed, with 90 per cent of pupils now EAL and 60 different languages spoken overall.
Over the years, Garton has seen his school expand steadily. "There hasn't been a summer where there hasn't been some building work taking place to try to give us some more space," the head says.
But space is something he is rapidly running out of. By September, Gascoigne Primary's roll will have increased to 1,200 pupils and the school will need to find room for half a dozen more temporary classrooms to deal with the increase in pupil numbers.
The lack of room to house the growing number of children plays on his mind, the head admits. The extra bodies will mean juggling priorities, and will mean losing a room dedicated to either music, special educational needs or helping to teach pupils English. But despite the strain his school is under, Garton does not think it is possible for a primary school to have too many pupils.
"It depends on the context of the school, of course, but I don't think size matters that much," he says. "You can have good small schools and bad small schools. It's a question of how well it is run and how it is led. You have to manage a big school in a very different way."
Whatever Garton is doing, it seems to be working. In its latest Ofsted inspection, Gascoigne was judged to be good with outstanding features - which, considering its intake and the number of pupils it serves, is little short of miraculous. He says inspectors even highlighted the care and attention given to individual children, an area many would expect to suffer given the size of the school.
In search of solutions
It is perhaps worth the secretary of state visiting the school so he can see how big schools can work well, despite such obvious constraints. Before coming to power, the Conservatives championed the cause for smaller schools. In the party's education policy document, upon which it fought the election, the Tories anticipated that free schools would be primarily "smaller schools" that would be financially viable with "fewer pupils".
But faced with a dramatic rise in pupil numbers, Conservative ministers have seemingly abandoned their pre-election pledge and have pointed to free schools as the answer to the shortage of school places. Indeed, at least #163;600 million of the money announced by the chancellor last year will be handed to such primaries and secondaries. After the promise of more cash from the Treasury, Lord Hill, parliamentary under-secretary of state for schools, said that the government was "building free schools and letting the best schools expand to meet demand".
And yet just 24 free schools are currently open, with a further 50 to 60 expected to open in September. The idea that free schools can plug the gap has been met with derision from both the Right and the Left, with critics calling on the government to loosen its purse strings further if it wants to avoid catastrophe.
Dale Bassett, research director at right-wing thinktank Reform, believes the coalition will be forced into a last-minute bail-out in order to provide for the extra pupils in the system.
"The money that was announced in the Autumn Statement will be nowhere near adequate to take the pressure off," Bassett says. "Sooner or later, the government will have to get its head around this.
"Local authorities will have to do what they can as they are statutorily required to find places for children in their boroughs, but they are already facing 25 per cent cuts to their budgets. The government will have to provide more money when it realises that academy sponsors and free schools will not be enough."
In many ways, this analysis was echoed by Russell Hobby, general secretary of the NAHT heads' union. He has called for a more practical response from the government.
"The government has found itself in an ideological bind," Hobby says. "Free schools are a very small solution to this problem and they take an awful lot of time to set up."
The quickest response, Hobby adds, would be to allow the best schools to expand - an idea that the government is keen to explore.
However, there is another wholly different and very controversial solution. And it is much cheaper than a government-funded building boom. The problem is that to make any headway with it would require the slaying of one of the most sacred cows in British public life.
Whisper it, but there are people out there actively promoting the idea of increasing class sizes in England's primaries.
Perhaps the most vocal adherent to this brave new world is the chief executive of the southwest London borough of Sutton. Earlier this year, Niall Bolger wrote to fellow London councils calling for them to help fight to increase the class size limit from 30 to 32. The public outcry that followed should have surprised no one. But increasingly, research is showing that the sacrosanct upper limit of 30 pupils in a room is one that needs rethinking. After all, it is worth asking what, truthfully, is the difference between a class of 30 and a class of 35?
According to a recent report from the Organisation for Economic Cooperation and Development, the body that oversees the Programme for International Student Assessment (Pisa) league tables, there is very little difference at all. The study looked at education systems in countries that perennially perform well in tests, and tried to pinpoint how they do it. One of the key findings was that the highest-performing countries place less emphasis on class size and more on improving the quality of teachers.
Guillermo Montt, author of the report, is clear that unless a country is prepared to cut its class sizes much more drastically than is possible in England for the foreseeable future - to 15 pupils or under - then very little difference is made in learning outcomes. "We find that school systems with smaller classes do not perform significantly better than those with larger classes," Montt says.
"In fact, we find consistently with other research on class size that reducing them does not yield much benefit when these reductions go from 35 to 25, or from 25 to 20," he adds.
Attempting to reduce class sizes is too complex and can have negative effects on an education system, he says.
"It means that more classes need to be taught, so teachers teach longer hours, reducing their time to prepare for classes and to reflect on what they have done. Or it means increasing the workforce, often to the detriment of overall teacher quality," he adds.
Should there be a limit on class size?
But why stop at 35? Could schools teach classes of 40, 50 or even 60? The DfE's own dramatic forecasts - that pupil numbers beyond 2015 will only increase, with numbers in 2020 expected to be up 21 per cent on 2010 figures - mean that we could have no option but to start talking in such terms.
Dylan Wiliam, emeritus professor at the University of London's Institute of Education, believes that the future of education is in bigger class sizes, with pupils from Year 3 being taught in classes double the size they are now. For Wiliam, the government's legal limit should be cut right down for the child's first three years of education. But after that, classroom numbers should be able to treble in size.
"If the government is going to be serious about a legal limit, then they should cut Reception, Year 1 and Year 2 to 15 pupils," he says. "But after that, I feel we have to get away from the magic numbers of 30 children per class and 40 minutes per lesson."
In Wiliam's future, primaries will be two-form entry, where the teacher does a full presentation that lasts 30 minutes to all of the 60 children in the two forms of, say, Year 5.
"After that, they are broken up into smaller, tutorial-style groups led by Year 6 pupils," he says, before adding: "If you are going to stand up and present to a class, it may as well be 60 rather than 30."
The move would mean that every pupil would be taught by those teachers with the most intimate knowledge of their subject. And the idea can be taken further, giving teachers even greater power, he says.
"A radical idea would be to enable teachers to apply to teach larger classes," he says. "To be able to teach larger class sizes you must be able to prove you are well above average as a teacher, and by doing so you get to teach a class of 45 or 50. In return, you get a 50 per cent pay rise.
"It is not a huge increase in costs, and attainment would go up as more pupils would be taught by the best teachers," Wiliam adds.
It would take a brave head, however, to start holding classes of 50, particularly in a primary school. In fact, it would be close to career suicide. No amount of praise from Ofsted would balance out the fact that parents brought up on a political and media diet centred on the class-size debate would run a mile from such a proposition.
You need travel no further than back to Barking to illustrate this point. For despite experience working with dizzying numbers of children, Gascoigne Primary sticks to 30 pupils per class.
Garton is clear: a school can be as big as you want it to be, but the number of boys and girls a teacher stands in front of cannot and will not go any higher.
"We feel that 30 children per class is already too many," he says. "We can have 50 or 60 per cent of children speaking another language in a class, so to increase that range by increasing the number of pupils would make it very difficult."
As the headteacher delivers these firm words, he glances out at his school. Quite where the extra temporary classrooms needed to house the 100 children who will be coming through the gate in September will go is anybody's guess.
The music room is about to go, and the library already sits in a portable classroom. Apart from the playground, it is difficult to see where Garton will find the space to put them. An increase in class size could give him some breathing space, but the headteacher is unlikely to be swayed.
Like many other schools in areas that are feeling the squeeze, Gascoigne Primary will just have to find the space. Garton and his teachers will have to do what they have been doing for the past 15 years. They will just have to manage.