Sam shakes his head and a swirl of silky black hair swings out. “That’s a lovely haircut, Sam,” observes the nine-year-old’s teacher, Ed. “Is it a bowl?” “No, it’s a step, number 2.”

“Did you have it done at the weekend?” “Yeah, my aunty done it. She’s a hairdresser and she’s got them clipper things.”

“Well, it really suits you.”

Pleased, yet embarrassed at the attention, Sam shakes his head again and ruffles the short hairs at the back. “It is a good haircut,” he concedes, “but you should have seen the one I had before!” Past haircuts, like past ice-creams, make thin memories.

Yet just watch Simon, swinging along with his floppy “curtains” and you can see how good it can be to have just washed your hair, be 17, 6ft tall and with your first girlfriend, or with Nat, who springs his dreadlocks out with an air of confidence as he skateboards around a corner.

Bad hair days, on the other hand, lower self-image.

Here is Angie, skulking along the corridors with her hood over her head. She is not taking it down, no way, never mind what the uniform rule is. “Don’t ask!” she snaps. If she ever gets her hands on that Debbie . . .

Her hair was meant to be platinum like Marilyn Monroe’s, with purple tips, but it’s turned out brassy with green streaks and, worst of all, a few clumps have fallen out leaving scabs on her scalp. The only way out may be a full shave, like the Sinead O’Connor of old. Now that is definitely against regulations.

Jim wishes he was not a redhead. It really gets you down always being called Copper Nob or Ginger and people commenting on your “other hair”. Oh, to be anything else, an unremarkable shade such as mouse.

Sarah does like not to be mouse - what an awful colour that is, she feels. Why won’t her parents let her dye it? She wishes her hair was a lovely red shade.

Eileen longs to have rippling curls like her sister Niambh, but her hair is as straight as paper and even the strongest perm falls out. Niambh, on the other hand, can never, even with the iron, get her hair to fall in shining sheets like Eileen’s.

Why doesn’t Fred Smith wash his hair, his colleagues wonder. Is there any need, in days blessed by the advent of medicated shampoo, to have dandruff falling gently like snow on suit collars? And you just know when Valerie Brown is in a bad mood: her hair slumps around her face as her shoulders slump down her spine. In the staffroom or playground, hair is a barometer of self-image.

In the 1970s, Colin Turnbull wrote a book about the Ik, a mountain people characterised by their cruelty and indifference to each other. The only time they actually enjoyed each other’s company was when they were grooming each other’s hair.

Which raises the question, what exactly did Debbie think she was doing when she poured twice the amount of bleach required on to Angie’s brunette mane? It couldn’t have had anything to do with that gorgeous boy in the sixth form, could it?