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 22 March 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. A self-completion survey was conducted of 2,638 students in years 9 and 12 from a selection of 11 government secondary schools in Perth. 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 12s and 28% of the year 9s 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 legalized. Although the CIN scheme applies only 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.