Objective: In the current study, we sought to identify distinct trajectories of symptom change and mid-treatment tailoring variables for the Unified Protocol for Transdiagnostic Treatment of Emotional Disorders in Children (UP-C) and Adolescents (UP-A), with the goal of providing empirical data to guide the implementation of adaptive and personalized interventions using this approach.Method: Participants were 94 youth ages 7-17 (M = 13.36, 56.40% female) who completed the UP-C or UP-A. Participants received a diagnostic assessment at baseline and completed symptoms measures at mid-treatment and post-treatment assessments.Results: Growth mixture modeling revealed three distinct classes of responders based on youth-reported and parent-reported symptoms of anxiety and depression, with two of these classes exhibiting significant slope variability. Overall baseline global severity, age, and comorbid social anxiety were significantly associated with class membership, while gender and presence of a comorbid obsessive-compulsive spectrum disorder were marginally associated with class membership. An 8-12% reduction in emotion disorder symptoms best predicted likelihood of post-treatment response.Conclusions: Results enhance our understanding of trajectories of response to transdiagnostic treatment and help to inform the development and implementation of more streamlined and personalized treatment approaches.