WE adults sit in the garden, munching barbecued sausages (burnt on the outside, a health risk on the lukewarm inside) and putting the world to rights. We eight have a dozen children between us, but it’s the two Year 11 girls we chat about.

Year 11 is the fifth year of high school in old money: conceivably the end of formal education for some kids and a milestone even for those who will return in September as sixth-formers. It’s worthy of a rite of passage . . . but, for heaven’s sake, let’s apply a little perspective!

It appears de rigueur to have a prom. I’m surprised these are often organised by schools, rather than the students arranging their own shindig. And the lengths some go to . . .

Some of Emma’s friends are paying a small fortune for a stretched Hummer to deposit them at the venue, while others are hiring an ex-fire engine. Shops have done a roaring trade in dresses, shoes and clutch-bags, as my credit card statement testifies.

I blame the evil of American-inspired capitalism for infecting Britain’s youth via imported TV shows and films. You can’t step into adulthood unless you’ve enjoyed the party to die for and spent a fortune.

Today, a magazine called Popular Prom is even distributed to Long Island and Queens high schools in New York, offering advice about tuxedos, limos, venues, after-prom activities (I imagine sleep would be good) and more.

The eyes of business people on this side of the Atlantic have lit up and they’ve fanned the myth. I’ll confess to Puritan tendencies, but I don’t mind frivolity. I am driven nutty, however, by wanton extravagance. Money spent on folderol could better support the poor. There’s also an unhealthy edge of one-upmanship.

Amazingly, I discover I’m not alone. There are “morp” groups (prom spelled backwards) in which students shun the “official” celebration and do their own – more personal and cheaper – thing. Six years ago, a New York high school stopped its backing of senior proms because it felt the events were now so beyond its control. The decision was prompted by students the previous year lining up a rented house in the swanky Hamptons for a post-prom party . . . at a cost of $20,000.

Emma despairs. “This kind of thinking is why that sixth-former in the strapless dress never gave you a second glance in 1981,” she hisses.

Perhaps I should change my ways and go to one of those prom-style events for adults that are now big business in the States. Popular Prom is trumpeting a “Flirt Pink Prom Dress” with soft sweetheart neckline. Wonder if it comes in a stretchy size 34.