Within days of watching a local production of West Side Story, children at a Suffolk primary had formed their own versions of the Jets and Sharks, the rival gangs in the Oscar-winning musical.
Pupils at Sir Robert Hitcham's primary, in Framlingham, were so impressed by the choreographed stand-offs that they copied them at lunchtimes.
Jenny Elphick, headteacher, said: "We had to stop them. We asked them to consider where it all ended in West Side Story."
In the show, Jets member Tony falls for Maria, the sister of Bernardo, a Shark. Bernardo ends up dead after Tony takes revenge on him for killing his best friend Riff.
Ms Elphick said: "I was concerned because lunchtime can be when children can feel even more vulnerable because there's less monitoring." She has introduced a "Friendship Stop" where lonely pupils can be befriended, and the school council has paid for two boxes of lunchtime games.
This week Ms Elphick was one of 140 teachers, heads and local education authority advisers who attended a conference in London which heard that lunch was the most difficult part of the school day.
Tim Brighouse, commissioner for London's schools, said: "Lunchtime is the most uncivilised part of the school day."
He hopes advice from Compton school, in the London borough of Barnet, will help solve the problem. Lunch at the technology college has been sliced into four half-hour slots between 11.40am and 1pm so that only a quarter of the school is at lunch at once.
Head Teresa Tunnadine said: "Behaviour is better. We haven't got that period in the day where pupils are kicking their heels with nothing to do."