The Department for Children, Schools and Families said boys aged between three and five had fallen behind their female classmates partly because nursery staff tried to curb their desire for boisterous play involving weapons. Boys were more likely to become interested in education and would perform better if encouraged to pursue their chosen play.

The advice has proved controversial with teachers' unions, which said that toy guns "symbolise aggression" and teachers were right to stop them being used. They also criticised the government for stereotyping boys.

The guidance, Confident, Capable and Creative: Supporting Boys' Achievements, said national data for 2004-06 showed that in nursery education, boys performed worse than girls across all areas of learning. It is a pattern which the government says continues up until GCSE stage. Better results can be achieved if nursery staff curb their "instincts" to stop boys from playing with toy guns and instead make better use of their interests.

"Sometimes practitioners find the chosen play of boys more difficult to understand and value than that of girls," the guidance states. "They may choose activities in which adults involve themselves least, or play that involves more action and a greater use of the available space, especially outdoors. Images and ideas gleaned from the media are common starting points in boys' play and 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."

It said this was unnecessary as long as staff helped boys understand and respect the rights of other children. "Creating situations so that boys' interests in these forms of play can be fostered through healthy and safe risk-taking will enhance every aspect of their learning," it said.

Beverley Hughes, the children's minister, said the guidance took "a common-sense approach to the fact that many children, and perhaps particularly many boys, like boisterous, physical activity". But Chris Keates, general secretary of the NASUWT teachers' union, warned that nurseries following the guidance risked incurring the anger of parents.

"I do not think schools should be encouraging boys to play with toy weapons," he said. "Many parents take the decision that their children won't have toy weapons. In addition to that, I think this is a clear example of gender stereotyping."

Steve Sinnott, NUT general secretary, said: "The real problem with weapons is that they symbolise aggression. We do need to ensure, whether the playing is rumbustious or not, that there is a respect for your peers, however young they are."