By Laura Clark
Children should be taught in single-sex classes for English because boys are being held back by the presence of girls, a study suggests.
It found that many boys are left 'hiding in the background', and perform up to a 10th of a grade worse when they are placed in mixed lessons.
And it claimed that the more girls there are, the worse boys do.
Lagging: Boys perform up to a 10th of a grade worse in English when they are taught in classes dominated by girls research has shown
The researchers from Bristol University found that the trend was particularly marked in primary schools but may also apply in secondaries.
The study, which is being presented this week at the annual conference of the Royal Economic Society, also found that in maths and science, primary school girls benefit from being taught in single-sex groups.
However, boys do better in those subjects with girls present, suggesting there is no way of organising classes to maximise exam results for both sexes.
The report said: 'It is not possible to increase the proportion of girls for both boys and girls, implying that a mix of the genders is optimal in both maths and science.'
For the study, researcher Steven Proud analysed the exam results of boys and girls at every state school in England between 2002 and 2004.
Most state primary schools are mixed-sex, although there are more single-sex ones in the independent sector.
Mr Proud found that, during English lessons, boys gained 'significantly' lower scores when there were girls present.
However, it made no difference to girls whether they were taught with boys or not. 'These results suggest that it may be beneficial to teach boys in single-sex classrooms for English,' Mr Proud said.
One explanation is that boys may feel they can 'hide in the background' in English classes if there are large numbers of girls, he added.
'Alternatively, the class may appear to be performing at an acceptable level while the boys are left behind,' Mr Proud said.
'An alternative mechanism could be that, since girls and boys learn in different ways, if the majority of the pupils are female, then the teaching may be focused towards learning styles that benefit girls more than boys.'
Schools minister Sarah McCarthy-Fry has suggested boys and girls should be taught separately for key subjects after expressing concerns that boys 'hog the limelight'.