ONE of America’s most exclusive boarding schools has been rocked by allegations of schoolgirl mayhem that make St Trinian’s sound like a convent. At Miss Porter’s School for Girls, where Jacqueline Bouvier Kennedy and George W Bush’s grandmothers were pupils, one clique of senior girls was named after a 16th-century Russian torture squad.

The girls, who called themselves “Oprichniki” - after the death squads set up by Ivan the Terrible to suppress his Russian enemies - are accused in an explosive lawsuit of orchestrating months of bullying that ultimately led to the expulsion of Tatum Bass, a senior girl at the Connecticut school.

A civil suit filed by Bass and her parents paints an alarming picture of life in an elite educational establishment that was founded in 1843 by Sarah Porter, daughter of a church minister and sister of the president of nearby Yale University.

The school quickly became a favoured haven for the daughters of the burgeoning American aristocracy. Its 6,000 alumnae include Gloria Vanderbilt, Laura Rockefeller, Lilly Pulitzer and several members of the Bouvier and Bush families.

The girls’ parents pay fees of up to $42,000 (£29,000) a year for an eclectic curriculum that includes art history, Chinese literature, skiing and “ultimate Frisbee”.

Yet according to Bass’s lawsuit, teachers failed to halt a startling pattern of taunts and threats despite repeated pleas from Bill Bass, Tatum’s father, who is the head of an insurance agency, and the girl’s mother, Nina, a paediatric psychiatrist.

“This is a hard-working kid. I hate to see this happen to her,” said Bill Bass. “We kept trying to make things right with the school.”

The lawsuit claims that Tatum was a popular student who had been diagnosed with attention deficit disorder (ADD). In her final year at the school, she was elected to a pupil council, where she became director of social activities. Trouble seems to have started when Bass proposed holding the senior prom - the traditional end-of-year dance - in conjunction with other schools nearby. An ensuing row about the management of the prom made her a target of the Oprichniki, a secret society.

The lawsuit claims that Oprichniki members took the lead in taunting Bass about her ADD, which had not been revealed to other students.

She was repeatedly called “retarded” and “stupid” and was humiliated in front of hundreds of pupils at a school dance. Some of her classmates threatened to boycott the prom.

The lawsuit contends the pressure became so great that Bass was driven to cheat in an art history test in late October. The suit said she was immediately overcome by remorse and confessed.

The exact circumstances of her expulsion remain unclear, but her parents claim that when they went to Tatum’s room to collect her belongings, her clothes had been tossed in a corner and a “for rent” sign hung on her bed.

Katherine Windsor, the headmistress, said in a statement that the suit’s claims, as reported in the local media, would be “defended vigorously”.

The row raises questions about how a group of teenage schoolgirls came to model themselves on Russian death squads that specialised in mutilation, impalement and dismemberment. The Oprichniki emblem was a dog and broom, a reference to their skills in tracking down their enemies and sweeping them away.

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