Data from police forces in England and Wales shows Class A drugs such as heroin and crack cocaine are among the illegal substances seized in more than 2,000 incidents and offences across the country over the last four years.
Teachers described the figures as a “worry”, and “the tip of the iceberg of what young people are encountering on the streets”.
Nationally the youngest person caught with drugs was eight years old. The data, from 34 police forces dating back to 2011, was obtained by the Press Association under the Freedom of Information Act.
Cannabis, the most widely used illegal drug in the UK, was involved in more incidents and offences than any other, 625, while cocaine was present in 27 cases.
Others confiscated by police included LSD, amphetamines, MDMA and ecstasy. There were two cases each of heroin possession on school premises in the West Midlands, Surrey and Greater Manchester - plus another incident in Hertfordshire.
The highest number of incidents and offences for the three complete years from 2011/12 - 2013/14 was 229 in Hampshire. There were 144 incidents at schools in Avon and Somerset, and 138 in the West Midlands.
Only four incidents nationally involved children under 11. This included an eight-year-old and a nine-year-old in Staffordshire primary schools who were caught with cannabis.
Chris Keates, general secretary of the NASUWT teaching union, said: “Any incident of drugs on school premises is worrying as it will often only be the tip of the iceberg of what young people are encountering on the streets.
“Teachers and school leaders are always alert to the potential for young people being involved in drug or alcohol abuse. Unfortunately, many of the programmes and specialist support on which schools could rely to assist them in supporting and educating young people in the perils of substance abuse have been cut under this coalition government.”
In West Yorkshire, 52 people had drugs confiscated while on school premises between April 2011 and December 2014. The youngest person to be caught with drugs on school premises was an 11-year-old schoolboy who had cannabis seized from him in 2011/12. A 12-year-old schoolboy also had the class B drug seized while on school land in 2014/15.
Of the 52 incidents, cannabis was seized on 48 occasions, cocaine twice, and LSD and central nervous system depressants both once.
According to North Yorkshire Police, there were 75 occasions where people had drugs seized over the three-and-a-half years. The youngest person caught with drugs was 12, though three 13-year-olds and 21 14-year-olds were also caught.
Of the 78 people who had drugs seized, two were school employees and 65 were pupils, with 11 classed as members of the public.
The seizures include four at a special needs school, six at a primary school, one at a boarding school and two at a grammar school.
Humberside Police recorded 61 drug offences in schools between April 1, 2011 and 31 October, 2014. The youngest person involved in an offence was a 12-year-old schoolgirl caught with drugs at a secondary school in 2012/13. In another incident in 2011/12 a 30-year-old groundsman had drugs seized at a college.
South Yorkshire Police did not respond to the request for information.