Most teachers tackle consistent lateness with punishments, detentions and stiff lectures. Hong Nguyen decided to tackle it with a diet.
The head of Year 9 at Our Lady's convent secondary, in Hackney, east London, resolved to help Elizabeth Afolabi, a 14-stone pupil, deal with her chronic lateness by ensuring that she lost weight.
"She didn't know what a calorie was," said Ms Nguyen.
"She didn't think there was anything wrong with eating three bars of chocolate and one packet of Monster Munch crisps at break.
"We wanted to give holistic support. We wanted to see if changing her attitude to food could also change her attitude to school."
Elizabeth, whose mother owns a restaurant, was placed on a diet-and-exercise regime. Ms Nguyen signed her up for after-school yoga classes. A diet was drawn up, involving copious amounts of fruit, vegetables and healthy snacks.
"The first time I gave her a raisin, she was almost physically sick," said Ms Nguyen. "She thought walnuts were made of wood. Now she wanders around school eating them."
Elizabeth, 13, has lapsed only once, when she ate a bar of chocolate, mistakenly assuming that, because it contained raisins, it was a health food.
In the three weeks since the programme began, she has lost six pounds. But, more significantly, her attitude to school has also changed. Previously, she saw lessons as interludes between snacks. But her new diet has given her increased energy levels, and her lesson-time concentration has improved significantly.
As a result, she has been told off less by her teachers. This, in turn, has led to renewed enthusiasm for school. Instead of being reluctant to arrive, she now comes to school in plenty of time.
"She used to stop off at the sweet shop on the way so she would be told off for lateness as soon as she came in and teachers would describe her as dozy," said Ms Nguyen.
"Now she's not being harassed by teachers so much, she finds lessons easier to cope with. She sees that what she puts into her mouth can have an impact on her future."
Elizabeth said: "I was always too tired and lazy to get up. I'd get detentions for being late and sometimes I'd fall asleep in lessons, and get detention then, as well.
"But the diet is better than detention. It doesn't feel like a punishment.
It feels like teachers want to help me. Now I'm not so tired."
Ms Nguyen was initially concerned that Elizabeth's classmates would mock her new, healthy-eating habits. But within days they were asking for their own packets of dried fruit.
Tolude Shomuyiwa, 13, was among them. "Celebrities have diet and exercise plans, so Elizabeth's like a celebrity," she said. "I'd be happy to eat raisins and things that don't taste that nice, if they do good things for your body."