It began as an attempt to avoid a Greek test scheduled for the Monday morning. Four 16-year-old pupils - three of them girls - broke into the prestigious Liceo Classico Parini in Milan at the weekend, while a fifth pupil was posted in the street to keep a lookout.

They set about sealing washbasins with silicone and cling film and left the taps running at the school where Alessandro Manzoni, author of the classic novel I promessi sposi (The Betrothed), was a pupil.

Thirty-six hours later caretakers found the school awash. Teaching equipment had been destroyed and 20 classrooms were waterlogged. Now the school will have to operate in shifts until the end of November while repairs are carried out.

The head claimed the damage, estimated at half a million euros (Pounds 350,000), had been caused by outsiders, but journalists soon discovered that the plan to sabotage the Greek test was an open secret, and the culprits were caught.

They now face up to three years in prison, though as they are under age, a community service order is more likely. Until sentenced they cannot be expelled, but their parents are likely to be asked to pay for the damage.

Classics teacher Aldo Scarpis, 52, whose test prompted the desperate gesture, said the culprits were just “normal kids”.

“There’s no point in my preaching to them,” he said. “We’ll just have to roll up our sleeves together, and get back to work.”