The intervention took the form of a randomized experiment, in which Treatment pupils were presented with data on their own misperceptions regarding cigarette smoking among their peers, followed by group discussions about normative misperceptions. Follow-up (n = 349) was conducted a year after intervention. Significant differences between Treatment and Control in misperceptions were found, not only regarding smoking, but also regarding alcohol intake and drug misuse. No significant differences were found in actual smoking prevalence, but other types of risk behavior, including different types of criminal offenses, were significantly less prevalent in the Treatment group, as were the numbers of self-reported situations in which pupils had given in to (imagined) peer pressure. The experiment demonstrated the existence of a ripple effect: the correction of misperceptions regarding one type of risk behavior influenced other types of misperceptions and risk behaviors as well. It is hypothesized that an important contributory factor to the success of the experiment is the absence of any moral judgment in the intervention. In 2006, the experiment was given the European Crime Prevention Award. (Published Abstract)