We do have our moments, we really do,” says Sue Tinson, closing the door on a pupil who is throwing a wobbly so that she can speak on the phone. But there is no concealing the pride and enthusiasm of this remarkable headteacher, who runs one of the smallest, most challenging and successful schools in the country.

The Serendipity Centre, the independent day school she set up in Southampton in 2006, has only 13 pupils and a maximum capacity of 15. They are all girls with statements of severe emotional and behavioural difficulties and several with other learning problems besides. Eight out of the 13 are “looked after” children. Many have years of truancy and youth offending behind them. Several have been permanently excluded from pupil referral units.

Since Sue set up the school with her husband Ian, who is business manager and head of IT, more local authorities have been paying to send their most difficult cases to her. Instead of going into full-time care, or prison, these girls will carry on with their education at their local college when they leave Serendipity at 16.

For their part, the girls say that Sue, her husband and small son, plus the staff, are providing the family life that they have never had.

Sue is well placed to understand her pupils’ problems. A looked-after child herself, she left school with one CSE in rural science and did not have the confidence to return to education until she met and married her husband. She gained a first in BEd, with a distinction in teaching, and worked for four years in a pupil referral unit in Southampton. There she found the opportunities for girls were limited, so she opened a school for them herself.

“These girls need both respect and physical space,” she says. And physical exercise too. As well as a personally tailored curriculum of English, maths, science, history, art and life skills, pupils must also follow an aerobic activity such as boxing, dance or PE.

Education this personalised does not come cheap, with annual fees of up to pound;65,000. There are more staff - 16, including five teachers and a home-link co-ordinator - than pupils. But compare it with the pound;250,000 a year cost of a residential school, let alone the public cost of lives of crime andor dependence on state benefits, and it begins to look like a bargain.

And the benefits are set to spread. Academics from the University of Southampton are working with the school to design, test and implement an enhanced curriculum for girls with complex needs that could be used in other schools.