Last week the reported that police were investigating Hong Kong International School after it expelled 11 pupils and disciplined others for drug use, without informing the police of its actions.

The police now say they are co-operating with the school on the matter, but declined to go into detail.

"I'm surprised they expelled the students," said Eric Chui Wing-hong, associate professor in the department of social work and social administration. "That's usually a last resort."

Chui said schools should give pupils more chances before they were expelled. "The purpose of a school is to help them to become law-abiding citizens," he said.

He said the stigma attached to being a drug user was particularly harmful in Hong Kong, where so much emphasis is placed on academic achievement.

"It's survival of the fittest, and once you're out [expelled], you're out," he said.

Kely Support Group, a non-government-funded youth charity that helps drug and alcohol addicts, has for years tried to push a more non-judgmental approach. "We believe that despite having a problem, [young drug users] can overcome it," said executive director Chung Tang. The group would not comment on the HKIS expulsions.

In April, a police source said English Schools Foundation institutions had seen an increase in the number of dealers selling drugs to schoolchildren. Three dealers were arrested.

The foundation said there was a small number of cases last year, but could not provide further details of the incidents. It said schools would call police only if there was trafficking involved.

The government released quarterly figures on Thursday showing the number of reported drug users was down from 4,055 in the first quarter of last year, to 3,337 this year. The number of drug users under the age of 21 went from 595 to 367.

HKIS said no one was available to comment on the matter.