The assertion is made in Boys and Reading, a report published by the Centre for Language in Primary Education.

The report's joint author, Sue Pidgeon, suggests that boys are poorer readers than girls because their experiences are more limited.

While girls are allowed to dress up as male and female characters, boys are discouraged from taking on female roles.

"Parents don't mind their little girls dressing up as pirates, but boys are not allowed to be princesses," Ms Pidgeon told BBC News Online.

'Ridiculous'

"Part of understanding what you read is about being able to see a particular point of view, and to do that we need to feel familiar with different characters, male and female.

"If boys are only offered a limited understanding when they are young, then we shouldn't be surprised if they have a limited understanding later on."

Ms Pidgeon, English adviser to schools in the London Borough of Lewisham, said she had based her conclusion on many years of observing primary school children.

But Nick Seaton, of the traditionalist Campaign for Real Education, described the idea as "ridiculous".

He said: "It's inviting cross dressing, which could cause gender confusion and damage a child.

"The research shows that boys learn to read well when they are taught properly, using the phonics method."