One in five schools thinks it has a problem with 'gang culture', a report by Ofsted has revealed.
This is related to the fact that around one in four schools said some pupils had bought knives or weapons into school at least once a term.
Some schools also told Ofsted they were worried about members of rival gangs fighting inside and outside schools.
However, a spokesman for Ofsted told BBC News there was not much evidence of widespread 'gang' problems in schools.
The spokesman added that it was important to deal with schools' concerns, but the problem wasn't necessarily as bad as some schools suggested.
"The number of accounts which reflected strong evidence, drawn from police or other local knowledge, of persistent gang behaviour outside school was very small," the Ofsted spokesman said.
Strong leadership needed
A government spokesman from the Department of Education and Skills backed this up: "Most pupils don't carry knives - in or out of the classroom," he said.
But the report did show there was bad behaviour and disruption in some schools, and "stronger leadership" was needed to tackle these issues.
It highlighted that the problems of drugs and weapons in schools varied hugely depending on what part of the country Ofsted looked at.
Schools minister Derek Twigg said: "We are supporting schools in showing zero tolerance to any bad behaviour."
Ofsted, the school's watchdog, said schools needed a stronger sense of community, better links with parents and stricter behaviour rules to stamp out problems.