The first attempt believed to be ever made by drug prevention researchers to investigate the long term effects of a school based curriculum that may have affected student's decisions on the use of drugs is reported here. This final report contains a short section in nontechnical language describing the study and its results, and a longer section providing the detail and language characteristic of a research report. The evidence from this study indicates that a curriculum that taught students to recognize when it is warranted to be uncertain has a desirable effect three years later on those student's beliefs and behavior concerning drugs. The curriculum was not developed for the purpose of drug abuse prevention and contained no examples or exercises dealing with drug abuse prevention. The most interesting finding, from the standpoint of drug abuse prevention, is the pattern of correlations indicating that students who can recognize when it is warranted to be uncertain about drugs report less hard drug use and more soft drug use. Another important outcome of the study is the finding that warranted uncertainty is a reliable construct which, irrespective of training, affects self-reported drug use. The discovery that drug use may be significantly affected by a relatively brief classroom-based training exercise that does not contain information about drugs has interesting implications for the development of prevention strategies. (Author/AM)