Background: Mental health professionals' decision-making practice is an area of increasing interest and importance, especially in the pediatric research and clinical communities. Objective: The present study explored the role of prior training in evidence-based treatments (EBTs) on clinicians' assessment and treatment formulations using case vignettes. Specifically, study aims included using the naturalistic decision making (NDM) cognitive theory to (1) examine potential associations between EBT training and decision-making processes (novice vs. expert type), and (2) explore how client and family contextual information affects clinical decision-making. Methods: Forty-eight clinicians across two groups (EBT trained = 14, Not EBT trained = 34) participated. Clinicians were comparable on professional experience, demographics, and discipline. The quasi-experimental design used an analog "think aloud" method where clinicians read case vignettes about a child with disruptive behavior problems and verbalized case conceptualization and treatment planning out loud. Responses were coded according to NDM theory. Results: MANOVA results were significant for EBT training status such that EBT trained clinicians displayed cognitive processes more closely aligned with "expert" decision-makers and non-EBT trained clinicians' decision processes were more similar to "novice" decision-makers, following NDM theory. Non-EBT trained clinicians assigned significantly more diagnoses, provided less detailed treatment plans and discussed fewer EBTs. Parent/family contextual information also appeared to influence decision-making. Conclusion: This study offers a preliminary investigation of the possible broader impacts of EBT training and potential associations with development of expert decision-making skills. Targeting clinicians' decision-making may be an important avenue to pursue within dissemination-implementation efforts in mental health practice.