BACKGROUND: Western Australia (WA) became the fourth Australian jurisdiction to adopt a prohibition with civil penalties scheme for minor cannabis offences when its Cannabis Infringement Notice (CIN) scheme came into effect on March 22, 2004. This study, part of the pre-post evaluation of the legislative reforms, aimed to measure the impact of the changes on attitudes and drug use of school children. METHODS: A self completion survey was conducted of 2638 students in years 9 and 12 from a selection of 11 government secondary schools in Perth. RESULTS: The students knew more about the risks and harms associated with cannabis than they did about prevalence of use and cannabis law. Half the year 12’s and 28% of the year 9’s had used the drug. Only 32% of students understood the term prohibition with civil penalties. Once explained, 70% of those who had never used the drug said they would not try it if such a scheme were introduced, 5% said they would try it and 24% did not know. Significantly more (11%) said that they would try the drug if it were legalised. CONCLUSION: Although the CIN scheme only applies to adults there was a concern that such a change would indirectly affect cannabis use by children. This pre-change study suggests this is unlikely but this will be monitored in the post change phase of the research.