Growing numbers of pupils are found carrying drugs and weapons every week at school, a study by Midland academics found.
A core of schools saw a significant increase in pupils with guns, knives and illegal drugs over the past seven years, according to the Warwick University research.
Teachers warned the trend was not restricted to gangs in large cities as provincial towns and rural areas also saw more youngsters arming themselves with weapons for "protection".
The study of 1,500 teachers by Dr Sean Neill, from Warwick's Institute of Education, suggested some schools faced severe problems.
"More teachers encountered offensive weapons more frequently in 2008 compared with 2001," the report says.
The National Union of Teachers, which commissioned the study, said schools should be "weapon-free zones".
Speaking at the union's annual conference in Manchester, NUT general secretary Steve Sinnott said: "The idea of bringing knives or guns into schools is totally, utterly unacceptable. Senior leaders in all schools need to get that message across very clearly to every single youngster.
"Teachers and parents want all schools to be weapon-free zones. We have got to make sure we are doing that. Some youngsters are telling their teachers that the biggest priority in their lives is to feel safe.
"Many youngsters say that the place where they feel most safe is their school.
"What other youngsters are saying is that one of the reasons youngsters carry a weapon is that they feel safer when they have got something to protect themselves with.
"We have got to get this message out: you do not make yourself safe by carrying a weapon, you make yourself more vulnerable."
Earlier this month, Cockshut Hill Technology College, in Sheldon, became the first in Birmingham with its own airport-style metal detector to scan pupils for weapons.
Headteacher Mary Kirkland said there had been no stabbings at the school, which has 1,500 pupils and 170 staff, and the decision to use detectors was "preventative".
At the NUT conference, Mr Sinnott said the survey revealed fewer teachers reporting "serious issues of discipline, of abuse, of damage to property" and classroom disruption.
But he added: "The picture, which seems to be in some respects very good, leads on a closer analysis to revealing that there is a polarisation taking place within schools. There was within a core group of schools greater incidence of violence, poor behaviour, disruption.
"In these schools the situation has got significantly worse."
The union warned the culture of drugs and weapons had spread beyond the well-known areas such as south London and Liverpool.
John Bangs, head of education at the NUT, said: "Do not assume it is just the urban areas exclusively - some of the toughest areas are in the country, on the outskirts of small and medium-sized towns."
The research investigated selected local authorities chosen to be geographically and socially representative. They were Barking, Bradford, Brighton, Cardiff, Cornwall, Derby, Hull, North Yorkshire, Salford, Sandwell, Suffolk, Swindon and Wrexham.
A spokesman for the Department for Children said: "It is important to remember that, as this survey shows, the overwhelming majority of schools are safe places to learn and work and the use of weapons within them is extremely rare. Schools are able to screen pupils for weapons using 'arch' and 'wand' metal detectors to ensure that such weapons are not taken onto a school site.
"We have also be given heads and school staff tough powers to conduct hands on searches of pupils.
"We back heads in taking the tough decision to exclude where behaviour warrants it."
Shadow Home Secretary David Davis said: "We have been calling for scanners in school for years. But the problem has just got worse over the last 10 years due to Government inaction.
"Labour's complacent approach to the rising tide of violence - and the drugs, knives and guns that fuel it - is betraying a whole generation of children who have to live with it in our schools on a daily basis."
Liberal Democrat home affairs spokesman Chris Huhne said: "These figures are a shocking revelation about the state of some of our schools. Even if some of this increase is due to better screening techniques, it is alarming that the means of street crime appear to be creeping into our classrooms."