Decades of research have demonstrated that relying solely on clinical judgment leaves one prone to a host of cognitive errors that compromise optimal decision-making. Clinical judgment appears to be particularly vulnerable to faulty heuristics and biases when assessing for pediatric bipolar disorder, as evidenced by staggering rates of misdiagnosis and overdiagnosis. Despite abundant evidence documenting the problems associated with clinical judgment, little research to date has explored the effectiveness of targeted interventions, or cognitive de-biasing strategies, for improving clinical judgment in mental health practice. The present project developed an intervention aimed at reducing cognitive-based error in the assessment of pediatric bipolar disorder. The study design was a randomized controlled trial and participants were mental health professionals (N = 79) with experience treating pediatric populations. The treatment and control groups responded to similar case vignettes and primary outcome measures were clinicians' diagnoses and treatment decisions. Unlike participants in the control group, participants in the treatment group received the cognitive de-biasing intervention and evidenced greater overall judgment accuracy, p<.0005. Participants in the treatment group also committed significantly fewer decision-making errors, p<.0005. Study findings can significantly advance the mental health field as improving clinical judgment, especially in cases of complicated diagnoses such as pediatric bipolar, are scientific and clinical priorities.