The principal of one of Auckland's top colleges says schools are struggling to keep drugs outside the gates - and has urged parents not to smoke cannabis in front of their children.
Russell Brooke, head of decile 10 Long Bay College on the North Shore, issued the warning to parents in a school newsletter before the start of the school holidays.
He said he wanted to "raise a concern, as a fellow parent and as a principal".
"Marijuana has become so freely available in society that the schools are struggling to keep it outside the gates," he wrote.
"As you can imagine, it isn't a topic schools like to raise with their community. However times are changing, societal attitudes to dope are relaxing, with many adults smoking it freely in front of children."
He urged parents to be "ever vigilant" and not to make "the common mistake of assuming 'not my child'."
Speaking to the Herald on Sunday, Brooke said he felt the need to write the warning because cannabis was "becoming much more acceptable" and its reach was spreading.
No school could say they didn't have a problem keeping drugs out, he said. "In fact, the more money in the school, the more likelihood it's there. And stronger drugs."
The recent debate around legalising cannabis for medical purposes had contributed to normalising attitudes around its use, he said. "There's so much push back that we've created a very confusing message for our children," Brooke said.
He was "pretty happy" Long Bay School was as drug-free as possible, but in the outside community "it's all around the place".
The school holidays had prompted him to warn parents and students alike about use of the drug during the break, he said.
"We've seen a bit on Facebook, we've had to give a few warnings to a few children around things, we've had a couple of kids dabble - it was outside school but we just felt we're a community, we want everyone to act as one big family," Brooke said.
"I don't want New Zealand to think Long Bay's a drug school, because that's not the case. But we're committed to keeping our families safe and our children safe, and we want to embrace the whole idea of talking as a community, educating the community."
He added: "I want parents to realise that you're raising a teenager, it's not about being their best friend, you've got a job to do. Especially that 11 to 14-year-age group."
The newsletter follows the revelation in the Weekend Herald two weeks ago that the country's largest secondary school, Rangitoto College, is set to bring in drug sniffer dogs.
"You have to be fairly naive to think there are not drugs in the community and one of the functions of the school is to make sure those drugs don't come here," principal David Hodge said.
New Zealanders consume an estimated 27,4400kg of natural and synthetic cannabis a year.