Up to eight students from a Sydney's Trinity Grammar School were asked to leave the school late last year following an incident involving cannabis on school grounds, according to the Sydney Morning Herald.

''The matter was reported to police and a record made, however, there was insufficient evidence to warrant a continuing investigation,'' a NSW Police spokesman said.

''Ashfield LAC maintained their involvement through the youth liaison officer as a proactive measure and the school conducted their own inquiry,'' police said.

The school's 2014 handbook states that students caught with alcohol or cigarettes were likely to be removed from the school, with automatic expulsion for those caught with illicit drugs.