Boys in nursery schools should not be discouraged from playing with toy guns and other weapons, the government says.
Inspectors say girls outperform boys from the age of five
In guidance for nurseries in England, the Department for Children, Schools and Families says staff should resist a "natural instinct" to stop such play.
It says role playing helps create the right conditions for boys' learning and could help them become more engaged in education in the future.
Teachers have condemned the advice, saying toy guns "symbolise aggression".
The guidance - entitled Confident, Capable and Creative: Supporting Boys' Achievements - says "practitioners" often find boys' chosen type of play "more difficult to understand and value than that of girls".
Boys regularly use "images and ideas gleaned from the media" as starting points in play, the advice says, which "may involve characters with special powers or weapons".
"Adults can find this type of play particularly challenging and have a natural instinct to stop it," the guidance continues.
"This is not necessary as long as practitioners help the boys to understand and respect the rights of other children and to take responsibility for the resources and environment."
Fostering these "forms of play" helps to "enhance every aspect of their learning and development", it adds.
Boys' underachievement in schools has been a source of concern for teachers and ministers.
Girls are more likely to get the benchmark five good GCSEs than boys and more girls do better at A-level.
But the National Union of Teachers (NUT) has criticised the government's advice on toy guns.
General secretary Steve Sinnott said the problem with toy weapons was that they "symbolise aggression".
"The trouble with weapons is that the toy gun is often accompanied by aggression.
"The reason why teachers often intervene when kids have toy guns is that the boy is usually being very aggressive."
Chris Keates, general secretary of the NASUWT teachers' union, said any nursery following the government's advice risked angering parents.
"Many parents take the decision that their children won't have toy weapons," she said.
"In addition to that, I think this is a clear example of gender stereotyping.
"I do not think schools should be encouraging boys to play with toy weapons."
But children's minister Beverley Hughes said the advice took a "common-sense approach" to the fact that many young children favoured boisterous, physical activity.
Many boys liked pretending to be superheroes or playing at "Star Wars characters with their lightsabres", she said.
"Although noisy for adults such imaginary games are good for their development as well as good fun."
But she added: "The guidance also impresses upon staff the need to teach children that they must respect one another and that harming another person in the real world is not acceptable."