Girls schools dominate this year's league table of the top independent schools' GCSE results, carrying off almost four fifths of the top scores.
Of the 53 schools where at least 99 per cent of entries gained a C grade or better, 39 were girls' schools. Twelve were boys-only and just two were co-educational.
The top school for the second year running was Withington Girls' School in Manchester, based on the percentage of exam entries gaining either A* or A grades.
Last night the Girls' Schools' Association said the case for single-sex education was now indisputable. Penelope Penney, president of the association and headmistress of Haberdasher's Aske's School, said the pupils needed little extra encouragement.
"We just feel that the single- sex argument is one that is borne out in the league tables. The fact is that both the single- sex boys' and girls' schools have done staggeringly well," she said.
In no fewer than 10 schools, every single candidate gained at least a C grade in every single subject entered. Nine of these schools were girls' schools and one, Westbourne College in Penarth, was co-educational.
At seven schools, more than four out of five exam entries gained either an A grade or an A*, the additional grade introduced last year for the top 3 per cent of candidates.
The figures were contained in the listings of GCSE results of 42,000 candidates in 625 independent schools which are members of the Independent Schools' Information Service, ISIS.
They showed that many of the schools, which are often highly selective, achieve remarkable results. More than four out of 10 entries were graded A* or A compared with 13 per cent nationally. More than nine out of 10 achieved C grades or better compared with 57 per cent nationally.
Candidates were entered for an average of nine subjects each, meaning that large numbers took far more.
David Woodhead, national director of ISIS, said: "By every measure, independent schools have outstripped national performances and demonstrated the wisdom of parents' investment in independent education," he said.
The performances of these top schools seem to be increasing despite a fall-off of the rise in GCSE pass rates nationally.
Last week, research commissioned by the co-educational schools' in the Headmasters' Conference showed that despite the excellent results achieved by girls schools they are not necessarily better than co-educational schools. Academics from the University of Manchester said that the key factor affecting the schools' performances was the extent to which they selected their pupils by ability.