A lawyer on the New South Wales north coast has questioned the wisdom of using police sniffer dogs outside schools.

The ABC has received complaints about the use of the drug dogs outside the Mullumbimby and Murwillumbah high schools in recent weeks.

Criminal lawyer Vince Boss said police need to rethink their strategy.

"For any search to be conducted on a person, they (police) need to have reasonable cause," he said.

"There's most definitely issues there pertaining to whether or not the search was actually a legal search to begin with.

"But secondly, I think the issue is the kids need to be advised that they do have their right to silence in relation to these matters, they do have the right to have a parent or a responsible person there with them when they're being interviewed.

"Going out and putting this level of distrust with the kids is not appropriate.

"I firmly believe the police have acted outside the guidelines of the act which governs them.

"The only thing this will end up doing is building distrust between the general populace of students.

"It's something that I think they haven't really thought through, that is actually quite damaging towards the police in the long term."

Police in the Tweed-Byron Local Area Command have made no apology for their actions.

Detective Inspector Brendon Cullen said police are acting in the best interests of the children.

"We do target where school children may be congregating before school," he said.

"We've had reports to us that children are turning up at school under the influence of illicit substances, and that's of great concern to us.

"It's about harm minimisation for those children.

"We've had some very positive feedback about the message that that sends to children who think that they can take drugs to school or consume them before school."