There were twenty minutes left on the clock. Idly he opened up his laptop and found the three nude pictures of Tamsin. There she was on her beach towel, squinting up into the sun, her big breasts slewed sideways. So different from the models in Nuts magazine. He wondered if 8S had ever seen natural breasts, mothers excepted. Perhaps they would be shocked, even disgusted, by breasts like Tamsin’s. Tamsin herself had hated the beach towel picture. Would it be possible to prevent that self-revulsion developing in his pupils by educating them about what their bodies might become? By showing them real female beauty, teaching them to look, shaping their tastes.

There was something oddly appealing in that idea, impossible though it was. Staring now at the photograph of Tamsin standing in front of the sea, Callum fell into a long reverie in which he was delivering a lecture to 8S. He was teaching the children about the camera’s relationship to the female body – specifically, the best lighting conditions for capturing the shape of a breast. Example 1A, the photograph of Tamsin, blown up to life-size on the smartboard behind his head.

And then there it was: an erection, his first in nearly two months. In what seemed like no time at all he was almost completely hard. Callum was so surprised that he didn’t stop to think about where it had come from. He looked at Tamsin’s breasts, then at the oblivious heads of the children, Verity Evanson’s neat white parting, Flick Chilcott’s thumb poking through the cuff of her damp, chewed jumper. Imagine if they could see what he could see. Callum was now so stiff that the pressure against the thick fabric of his flies was actively uncomfortable. A ridiculous phrase – ‘irrepressible erection’ – came into his head and played itself over and over, absurdly exciting him further. He had an irrepressible erection. Nine pairs of eyes on Tamsin’s tits, full of shy excitement. He would make them look. Callum nudged his erection with his knuckle and it felt glorious.

‘Mr D?’

At the sound of Hugh Brodie’s voice, Callum’s erection rapidly deflated.

‘Yes, Hugh?’

‘Sir, I know you said not to do the English into Latin on question 4c), but I want to know, what if the other one looks really nasty?’

Callum hastily closed down the photograph of Tamsin and motioned for Hugh to come and show him the problem, hoping the boy wouldn’t notice the tremor in his hands.

He spent the rest of the day suspended between shame and giddy relief. His impotence had granted him false immunity: because there had been no erection, he had allowed himself to believe that his impulses were not sexual. Yet he knew better than anyone that arousal was not always accompanied by erection.