When I came to Tunbridge Wells I couldn’t believe it,” Terri says. “All those neat houses and neat lives. Milly-Molly-Mandy land. Safe, normal, average. Its blandness was so exotic to me.”

Terri, who came from an abusive background and a childhood spent in colourful foreign locations, courtesy of her father’s job in the armed forces, wants nothing more than to disappear into a sea of lives and faces where no one is singled out for special treatment, where life is predictable and people unsurprising. When school reports tell her that her children are average, she is pleased. Average is safe.

Ervin, on the other hand, is tearing his hair out. His beloved son Jamie is not only mildly dyslexic, he is of “average intelligence”.

For a man who has made a good living from outwitting other sharp operators on a City trading floor, “average” means “will never amount to much”.

What’s more, it seems to be a confession of genetic failure: dyslexia is special needs, it’s a kind of misfortune, but being average is nothing special at all. And if you are nothing special at all, what are you?

Barry is a nice boy. He behaves well, he does his homework, he attends school regularly. But sometimes, says his mum Sandra, “it’s as if I feel the teachers don’t really see him”.

“He’s not a problem, but he doesn’t win any prizes either. Once they’ve said he’s average, that’s it. They’ve ticked the box,” she sighs.

When Barry’s parents went to discuss his GCSE options, the staff were very relaxed. Barry could stay at the top of the middle set in maths and get at best a B, or he could go up to the top set where he might get, yes, a B.

He could plug away at history GCSE where his coursework was quite adequate, or he could stick at geography where his coursework was “fine, quite ok”. It was a deafening chorus of tepid approval.

Naturally, everyone is pleased that Barry doesn’t get into trouble. But sometimes it does seem, just as it says in the Gospels, as if there is more rejoicing over one sinner who repents than over a thousand who never stray.

Lucas is a very bad boy in Barry’s class. On the rare occasions when Lucas is not in the teacher’s face, he is probably messing about with someone else’s stuff. “He’s a prat,” says Barry, who avoids him and tries not to think about him either.

Last week, though, Lucas got a merit. What for? For “conforming to correct behaviour” for a whole day. This forced Barry and his Mum to think about Lucas.

How come Barry has never, not once, got a merit for conduct although he has never ever done anything wrong? And now, the first time Lucas refrains from doing anything wrong, he gets a merit.

Far from feeling part of the kind of nourishing normality that Terri wants for her children, averagely good Barry now feels raw and unappreciated.

A wise teacher would take some time in a tutor group to emphasise that grades of academic achievement are no more than markers and that each individual has inalienable value in and of themselves.

But, in the nature of things, most teachers are themselves only averagely wise.