Police were involved in 377 incidents at schools last year, according to the NSW Bureau of Crime Statistics and Research. This is the worst figure recorded since 2003.

Nine out of 10 incidents (340 offences last year) occurred during school hours - an average of 1.7 per school day.

The number of incidents, which include dealing or trafficking as well as use or possession, has risen steadily over the past seven years and more than doubled since 2008.

Father Chris Riley, founder of Youth Off the Streets, said the actual rate of use was far greater.

"They're 380 incidents that have been detected and responded to. It's pretty minimal. Our experience is that there is a lot more, but kids can cover up pretty well," he said.

The rise has been driven by an increase in offences involving use or possession of cannabis. In 2014, more than 75 per cent of offences were cannabis-related.

The Department of Education said the data captured incidents occurring outside of school hours and persons who were not students.

"Some of these incidents have occurred when the schools are closed, on weekends and during holidays. The incidents are for all schools and include incidents on non-government school grounds," a spokesman said.

Last year's offence rate, a figure which accounts for population size, rose to 5.2 per 100,000 across NSW, up from 2.4 per 100,000 in 2008.

However, the state average obscures dramatic variation between NSW regions.

Lismore has one of the state's highest offence rates at 45 incidents per 100,000 population. Police were involved in 20 incidents in Lismore schools last year.

The highest number of incidents were recorded in Shoalhaven on the state's south coast (22 incidents or 22.7 per 100,000).

In Greater Sydney, Penrith and Campbelltown recorded offence rates above the state average (5.9 per 100,000 in both local government areas). Police were involved in 11 incidents in Penrith schools and nine incidents in Campbelltown schools last year.

The rise in offences related to possession or use of cannabis was not limited to schools, BOCSAR deputy director Jacqueline Fitzgerald said.

"Between 2013 and 2014 possession/use of cannabis increased 17 per cent across NSW", she said.

She confirmed the data included government and non-government schools, and incidents that did not necessarily involve students or teachers.

The Department of Education said it had a robust drugs in school policy that required schools to plan and execute responses to all drug related incidents.

"There is an emphasis on prevention through drug education and safe and supportive school environments, and intervention and support for students who may be involved," a spokesman said.

But Father Riley criticised schools and principals for not doing enough. He pointed to a "real gap in education", saying every school must have a counsellor who deals with drug and alcohol issues.

"They need to make sure the curriculum covers drug issues in a realistic way without sanitising drug and alcohol issues," he said.

A NSW Police spokeswoman said its officers attended schools when asked to investigate alleged drug-related offences.

"If an offence has taken place, where possible, students will be dealt with under the Young Offenders Act," she said. "NSW Police work closely with schools across the state, with student and youth liaison officers based at every local area command."

The Association of Independent Schools of NSW declined to comment, saying it was not possible to identify the school type in the data.