CHEERS and sobs met the publication on August 13th of A-level results, the school-leaving scorecards that tell British 18-year-olds whether they have made the grades required to get into university. As ever, many of the most successful schools in the state sector were grammars, which select pupils on the basis of their academic ability. Grammars’ supporters see them as engines of social mobility, pointing out that they educated five consecutive prime ministers between 1964 and 1997. Detractors argue that their benefits accrue mainly to the middle class, rather than the poor (less than 3% of grammar-school students are hard-up enough to get free school meals, compared with 16% of pupils across the state sector).

The critics had the better of the argument in the 1960s and 70s, when most grammar schools were converted to non-selective comprehensives. From a peak of 1,298 in England and Wales in 1964, only 163 grammars remain, all in England, with a high concentration in the south-east. (Northern Ireland has a further 69.) No new one has opened since Labour banned their creation in 1998, a position that the ruling Conservatives support, albeit with some dissent among their backbenchers.

Yet despite the cap, the number of pupils educated in grammar schools has been steadily rising. Their classrooms hold 33,000 more pupils than in 1998. Nowadays 5.1% of children in England and Wales are educated at grammars, a higher proportion than at any time since 1978 (see chart).

Although setting up brand-new grammars is banned, there is no restriction on how far existing ones may expand. Many have therefore called in the builders. In the London suburb of Sutton, Nonsuch High School (which sits on a plot near the site of Henry VIII’s Nonsuch Palace, so called because it was said that no building could rival its magnificence) used to take about 150 pupils a year. In 2000 it built a new block, increasing its capacity to 180. A red-brick extension is currently under construction, so that September’s new intake can go up to 210. One driver of grammars’ growth is population change. The number of babies born in England and Wales has yo-yoed between about 600,000 and 700,000 a year since the 1970s. When the birth rate has been low, local authorities have closed or merged small schools. When it has been high, as it is at the moment, rather than open new schools they have gone for the cheaper option of enlarging existing ones—particularly grammars. That is partly because of demand from parents, who are impressed by the good exam results that grammars grind out. Last year Sutton’s 16-year-olds chalked up the fourth-best results in the country, partly thanks to the borough’s five grammar schools, which parents from other parts of London try to get their children into. “Grammars import more children from out of the borough than is currently desirable,” says Tim Crowley, a Conservative councillor. Grammars also tend to be relatively easy to expand. For one thing, they are more likely than comprehensives to be located outside city centres, with more space to grow. And they usually have smaller classes, giving them spare capacity, says Tracey Hartley, the acting head teacher of Nonsuch. Three years ago Sutton asked all its schools to make plans to take on more children. Two of the four schools able to do so, including Nonsuch, were grammars. The schools themselves are keen on expansion: the economies of scale mean a wider range of subjects can be taught, Ms Hartley says.

The central government has made it easier for grammars to swell. In 2012 the Conservative/Lib Dem coalition tweaked the rules to allow all schools, including grammars, to grow on their existing sites without consulting their local authority. And a majority of grammar schools now have “academy” status, which gives them greater autonomy over matters including expansion. “Local education authorities were a dead hand. Many of them were Labour-controlled, who ideologically didn’t want grammar schools,” says Robert McCartney of the National Grammar Schools Association.

In 2012 grammars were given the right to expand onto different sites if they could show that the new buildings constituted an “annexe, extension or satellite” of their existing operation. An application by an all-girls grammar in Tonbridge, Kent, to build an annexe ten miles away in Sevenoaks was turned down in 2013, partly on the ground that it would have catered for both boys and girls. The school has put in a new application for a girls-only annexe.

Whatever the decision in Kent, expect grammars’ stealthy expansion to continue. Mr McCartney believes there is “significant” scope for many to grow further. At Nonsuch, which was built in 1938 to take fewer than 100 pupils a year, there is already talk of expanding the intake to 240.