Hundreds of children are bringing drugs, including class A substances, into UK schools every year.
Figures obtained by Sky News show more than 1,000 pupils have been caught carrying drugs in schools over the past three years.
Among those pupils, 27 were found with class A drugs.
Some 93 pupils were charged with drugs offences, including six at primary school.
The figures come from 32 of the UK's 44 police forces but do not include some of the country's largest, including the Met and Greater Manchester.
Campaigners are concerned drug use among children is a problem that is being ignored.
Camila Batmanghelidjh, founder of charity Kids Company, which works with children from deprived backgrounds, said: "A lot of (children) are born into households where their parents are prolifically abusing substances.
"What we're seeing now is that eight and nine year olds are beginning to smoke weed and skunk and then they go on to harder stuff.
"Unfortunately, in a lot of neighbourhoods, children see the drug trade as a completely legitimate way of making a living.
"It's become so familiar and in a way it's become so normalised because children are completely surrounded by adults who are using."
One 18-year-old who was addicted to cannabis for three years said drug use had been common among children her age.
Jade Clement, from Poole, Dorset, who now campaigns for the charity Fixers , said: "I always had a friend that I was smoking with. We constantly had to lie, tell our parents we were going to the cinema or swimming - anything like that so we could get a tenner.
"I was meant to be in school ... (but) if I had weed left over from the night before then I wasn't going in.
"I couldn't be bothered. It didn't interest me (and) the only reason I went in was so I could plan (to take drugs) with my friends ... that's all school was really about."
Schools in affluent areas say they are equally concerned about the likelihood their pupils will be exposed to drug use.
At The Hall, a prestigious independent school in north London, former addicts are invited to speak to pupils to warn them about the dangers of drug use.
Thirteen-year-old student Callum said: "It's quite daunting that I'll be offered drugs in the next three to five years. It leads me to think, 'What will I say? Will I be pressured?'"
The Government said banned items like alcohol and drugs have "no place whatsoever in the classroom".
A Department for Education spokesman said: "We've introduced a range of powers for teachers to ensure discipline, behaviour and safety are maintained.
"Teachers can now search a pupil without consent when they suspect they may be in possession of a prohibited item.
"Changes to the system mean a school's decision to exclude a pupil cannot be reversed by an appeals panel.
"Our guidance also makes clear that teachers can use force to remove disruptive pupils from the classroom when necessary."