A typical Kentish town, with its grammar school at one end and its secondary school at the other, is a throwback to the Bad Old Days, or the Good Old Days, depending on what your views are on academically selective state education. If Theresa May’s plans go ahead, the whole country might look something like this.

In my childhood home town of Sandwich, Kent, the two schools, Sir Roger Manwood’s grammar school and the Sandwich Technology School, have staggered going-home times to avoid the fights on the station platform that used to happen every afternoon. Their uniforms are tellingly different: the Manwood’s students wear smart blazers and ties, the Tech ones wear casual black polo shirts and black jerseys. There’s a slight shiftiness in the afternoon atmosphere. Self-conscious Manwood’s girls change out of their uniform as soon as they get home from school in order to avoid being mocked by ‘Techies’ in the Co-op. Tech children sit on the green after school and leave all their litter behind, because there’s a caretaker at their school whose job it is to pick up all the rubbish. Manwood’s students go home with about three times as much homework as Tech students.

From the outside, a prospective parent would be forgiven for mistaking which school is which. The Technology School is the shiny, swanky one, with cinema, sports hall, AstroTurf, its own football academy and its own windmill providing electricity. The grammar school is more shabby-looking, after progressive anti-grammar Labour councils were mean with funding. Lots of parents, looking round the two schools, actually prefer the Tech, which is both dazzling to look at and known to be a kind establishment that aims to look after the needs of every child.

Ysenda Maxtone Graham discusses grammars with Toby Young on the podcast

But it’s not the superficiality of the buildings that matters most to motivated children: it’s the intellectual climate. At grammar schools, teenagers feel that it’s not uncool to work hard. That hard work gives them more opportunities in later life. I’ve come across many groups of siblings whose lives have gone in totally different directions, according to whether they did or didn’t go to the grammar. One said to me last week, ‘My two brothers, who went to Simon Langton grammar school in Canterbury, have done so well, whereas I struggled, to say the least. I wish I’d had that opportunity. Same with my best friend: both her brothers passed the Kent Test. One’s running the motorways in Kent, and the other’s a teacher. She went to Herne Bay High and she’s now a hairdresser.’ Thus futures are all too often mapped out in the county of Kent. The thing we will never know is, what would have happened to those people if they had all gone to a comprehensive instead? Would one have been dragged up, or the other two dragged down? Or would nothing have turned out differently?

Any Kentish parent, embarking on the quarter-century of insomnia that is putting one’s child through education in this country, quickly becomes acquainted with the dread words ‘the Kent Test’. It’s the county’s own voluntary 11-plus exam, designed to siphon off the top 25 per cent of the population. (This is quite progressive: it used to be only the top 10 per cent.) Theresa May’s idea is that poorer children would pass this test, but the truth of English state education is that wealth and academic attainment are closely correlated — a trend that sets in during primary-school years. Those who do best in the 11-plus will, disproportionately, be those from the wealthiest families. Just how this helps the ‘just managing’ classes is a bit of a mystery.

If you’re the kind of person who has academic ambitions for your child and is not rolling in money, passing the Kent Test becomes an obsession at an early stage. Time to buy a batch of online past papers from the Kent Test website; time to book an after-school tutor for regular sessions on maths and verbal and non-verbal reasoning (again, a struggle for the ‘just managing’ classes). Time to make sure, also, that your child is at an ambitious enough primary school. One mother I spoke to was told by a friend of hers, ‘Get your child out of this village school: no one passes the Kent Test from here.’

For parents who can afford to send their children to prep schools, grammars are a godsend: why pay fees if there’s a fabulous, free, high-achieving grammar school on the doorstep? At local private prep schools, almost every child is put in for the Kent Test as a matter of course. Nationwide, about one in nine grammar school pupils has arrived from a private prep.

Very early in September each year, about half of the children of Kent, still dazed and woozy from the August heat, sit the Kent Test in their own schools. It’s an hour-long multiple-choice exam with 60 questions and there’s no point in sitting it if you don’t know your times tables. It’s also useful if you’re the kind of person who shines at verbal and non-verbal puzzles. At the end of the exam, candidates have to write a short essay: this is only looked at if the candidate is borderline pass/fail.

There are enough grammar-school spaces in Kent for one in four children. So there’s a lot of unrealistic expectation. Quite a bit of bribing (of children) goes on. There’s a well-known Kentish expression: ‘The selection bicycle.’ This is the new bike promised by parents as a reward for their children who pass the Kent Test. Many children — and their parents — are disappointed. The appeals process is anguished and drawn-out. Desperate parents call in lawyers if they’re really fed up.

It matters because, as successive studies have shown, the presence of grammar schools normally means the other schools are worse than they would be in mixed-ability areas. The best teachers applying for jobs are much more likely to apply to the grammar schools, where students are well-behaved and actually want to learn. So a creaming-off of teachers as well as of pupils goes on. I’ve heard of non-grammar schools in Kent having a director of music who couldn’t play the piano, just the guitar. Of A-level teachers unable to teach to an ‘A’ grade.

The selection process can have a demoralizing effect on those it excludes. ‘I can’t do that, because I’m thick,’ said a Tech girl to a friend of mine who went into the school recently.

‘Why d’you think you’re thick?’ my friend asked.

‘Because I didn’t pass the Kent Test.’

Academic selection is still so taboo in the state world that it’s easy to forget that in the world of private education it’s as rife as can be. Children as young as three are ‘assessed’ for the top pre-prep schools. My cousin’s three-year-old daughter memorably exclaimed ‘That’s a Giacometti sculpture!’ on the staircase of Thomas’s Battersea, and still didn’t get in.

The Kent Test aims to be a test of raw intelligence, not attainment, but it’s almost impossible to design a test that doesn’t take attainment into account. What if the cure for cancer is locked in the brain of a boy who lives on a council estate where his mother is dealing drugs on the kitchen table, so there’s no table for him to do his homework on? The best thing about grammar schools is they can pluck such a person out of the mire and help him or her to a worthy future. I’ve heard countless stories of such rescues: boys from hopelessly broken homes who have become successful solicitors thanks to grammar-school rescue. Looking at those black-jerseyed ones coming out of school in the afternoon, I can’t help searching for the unnoticed genius who didn’t quite make it.