Orthodontic studies over several decades have found generally inconsistent opinions among dentists when evaluating orthodontic treatment need. There has also been recent concern that dental school education does not sufficiently prepare dentists to diagnose malocclusion and make appropriate referrals of potential orthodontic patients. The purpose of this study was to investigate the efficacy of using the index of orthodontic treatment need (IOTN) as a tool to improve dental students' ability to assess orthodontic treatment need. Fourth-year dental students were randomly divided into control, sham-control, and experimental groups stratified for mean grade point average. On 2 occasions, the subjects evaluated 30 orthodontic study models with a gold standard previously established by an expert panel of 15 orthodontists for orthodontic treatment need. The experimental group reevaluated the models after IOTN instruction. Kappa statistics, sensitivity, and specificity were calculated for each subject. Analysis of covariance (ANCOVA) showed that the experimental group had significantly higher agreement with the expert panel after IOTN training than did either control group. IOTN is a promising teaching aid for improving educational outcomes for orthodontic referral.