GIRLS attending single-sex schools far outperform their contemporaries in mixed education, an analysis of government data have found.

The research by the independent Girls’ Schools Association (GSA) shows that this year 56.7% of their member schools’ A-level results were at grade A, compared with 48.9% at coed independent schools.

At GCSE the margin was wider still, with 68.5% marked A or A* compared with the mixed figure of 54%.

The research, based on figures from the Department for Children, Schools and Families, reflects a trend that has been apparent for at least the past four years.

In recent decades single-sex education has declined in popularity, with the number of schools falling from nearly 2,500 30 years ago to about 400. In the past decade alone, some 120 independent schools have gone co-educational.

Some of the best-known former boys’ schools, such as Wellington and Uppingham, are now mixed, although others, including Eton and Winchester, have remained boys-only.

Girls’ schools have been more likely to resist going co-educational. Advocates of the system believe that in mixed classes girls are more likely to be inhibited and reluctant to voice their opinions openly.

Girls in single-sex schools are also more likely to take A-level subjects which in mixed schools have traditionally been seen as the preserve of boys, such as science and maths.

Last year, 72.5% of pupils in the GSA schools won A grades in maths A-level while the figure was 64.9% for girls in their mixed equivalent. The national figure was nearly 30 percentage points lower.

Separate research by the Girls’ Day School Trust, an independent chain, has found that the proportion of their pupils taking science subjects at A-level is more than double the national average.

Vicky Tuck, president of the GSA and principal of Cheltenham ladies’ college, said girls schools “have a brilliant track record in helping pupils attain”.

However, Richard Cairns, headmaster of the mixed Brighton college, said boys and girls complemented each others’ learning.

“Boys will focus on what’s going on in the killing fields, and girls will think, ‘What’s the impact [over] the next 40 years when there’s no father at home?’ ”

Rebecca Ogilvie-Smith, from Oxfordshire, who last month scored top grades in all her AS-levels at Cheltenham – while also winning top grades in her French A2– said attending a single-sex school had taken off “a certain pressure” which the presence of boys can bring.

“There is a very intense feeling of community and it is not judgmental,” said Ogilvie-Smith. “Your focus is not on how you look.”

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