Likewise, try telling a 14-year-old that she should learn to use a washing machine, answer a phone politely and keep an account of her spending so that she has these skills for the future. The future? You mean this afternoon? Mum, lighten up!
New parents and teenagers have something in common: an immunity to the hard, unwelcome truth about what lies ahead. And it's just as well, otherwise the population would diminish and teenagers would have the future to depress them as well as spots, exams and unrequited lust.
But another species with the same immunity is the trainee teacher. They, too, can ignore dire warnings about what is to come, thinking they can inspire the uninspirable and thrill the unthrillable. They like new parents who decorate their lounge in apricot white and put their DVD player at floor level, and like the teenager who risks early deafness with his music and early death with his junk food won't listen to anyone.
I recall being like that. "Pace yourself," someone told me when I was training and as green as guacamole. "Don't plan all your lessons as all-singing, all dancing performances. Keep the odd worksheet to hand." I could hardly keep the sneer under control at the "W" word and it wasn't until two years in, when only intravenous caffeine kept me awake, that I learned my lesson.
Similarly, I was told: "Don't try to be their friend." Ha! Surely she was only saying that because she didn't know how to relate to teenagers. I was going to revolutionise the profession by being a magical Jean Brodie character and the kids would cluster around my desk after lessons to talk about their problems. It was only after being humiliated by a pupil that I toughened up. She hissed, in the midst of paper-aeroplane, pen-stabbing chaos: "Just give them detentions, Miss. Don't worry about them not liking you."
Some things no one mentioned. No one warned me that one glass of wine with dinner would mean I'd ditch my marking and watch soaps. No one mentioned that I'd consider voluntary catheterisation to deal with daytime bladder needs. No one told me about the mug hierarchy. And nobody talked about tummy bugs, laryngitis and perennial colds.
It's no wonder. They knew then what I know now that I wouldn't believe a word. I was immune to the truth and arrogant to boot. Me, get colds? You must be (achoo!) joking!
* Fran Hill teaches at an independent school in London