Research shows that social norms interventions, which aim to educate individuals and groups on their actual attitudinal and behavioural norms relating to alcohol, cigarette and drug use,incur some success in reducing positive attitudes to substance use and rates of substance use. The research aimed to investigate the extent of misperceptions relating to peer substance-taking attitudes and behaviours amongst a sample of school aged youth (n = 80), and was undertaken as a pre development study to a large scale social norms initiative in Irish schools. The study found evidence for the existence of misperceptions relating to cigarette, alcohol or illicit drug use, with no significant differences pertaining to gender and school type. Attitudes to, and self reported cigarette and illicit drug use, tended to be more conservative. Statistically significant differences were found between participants self usage and peer usage of cigarettes, alcohol, cannabis and other illicit drug usage in the past 30 days. A statistically significant main effect for self reported cannabis use and school type was found. Findings were used to guide the development of a culturally appropriate targeted social norms intervention. (Contains 5 tables.)