ABSTRACT Background and Objective Increasing numbers of adolescents and young adults suffer from serious mental health conditions with onset primarily in childhood or early adolescence. Anxiety and depression have significant negative and long-term effects that interfere with developmental tasks if not successfully treated. Research indicates that approximately 50% of youth suffer from a mental health disorder and approximately half experience remission in psychotherapy (Blanco, 2008; James, 2020; Kessler, 2005). An evidence-based model, TEAM-CBT, was designed to improve outcomes in psychotherapy by incorporating empirically-supported treatment components including: Testing, Empathy, Agenda Setting, and Methods. It was expected that youth treated with TEAM-CBT would experience significant reduction in depression and anxiety symptoms from pre-test to post-test. The second hypothesis predicted that patients completing more sessions would have better outcomes. The third hypothesis was that within each session, post-session levels of depression and anxiety would be significantly lower than pre-session levels. It was also expected that therapists who were perceived as more empathic by their patients would have better outcomes. Finally, two exploratory questions were included: 1) Is there a correlation between age and treatment outcome and 2) What is the pattern of treatment response over sessions? Methodology This naturalistic, retrospective study used brief assessment data for 116 adolescents and young adults treated on an individual basis in a group psychotherapy practice. An intention-to treat model was used to compare pre-test and post-test scores on mood levels and within-session change in symptoms. Treatment outcomes were measured as changes in depression and anxiety levels as assessed by the Brief Depression and Anxiety subscales of the Brief Mood Survey (BMS) which were self-administered before and after each therapy as part of routine treatment (Burns, 2010, 2011). T-tests and ANOVAs were used to test treatment effects, including changes between the first and final sessions, within-session change, and the pattern of treatment response. Correlation analysis was used to test the association between age and treatment outcome. Findings A total of N = 116 patients’ data was included in the analysis. Both depression and anxiety scores were significantly lower at post-test compared to pre-test. Pair-wise t-tests found that anxiety scores were, on average, 5.67 points lower at post-test (p < 0.0001) which equates to a large effect (Cohen’s d = 1.10). Depression scores were, on average, 5.39 points lower at post-test (p < 0.001), which also equates to a large effect (Cohen’s d = 1.17). The majority of adolescents and young adults achieved clinically significant improvement, with 87% of youth no longer meeting criteria for clinically significant symptoms of anxiety and 80% of youth for depression symptoms. There was no correlation found between the number of sessions received and the treatment outcome. Within-session symptom reduction was clinically significant in each of the 10 sessions. A test of normality was run for hypothesis four suggesting that nine out of 10 therapeutic empathy scores were not normally distributed. Values were skewed to the right of the mean. Due to the skew the therapeutic empathy scores could not be used in hypothesis testing. Finally, an ANOVA analysis demonstrated a curvilinear pattern of treatment response in which the largest symptom reductions occurred over the first five sessions followed by a plateau from session five to six and smaller significant change from session seven to session 10. Implications These results suggest that the TEAM-CBT framework is highly effective for youth seeking treatment for mood disorders in an outpatient group practice setting where treatment is delivered one-on-one in person and/or virtually. Significant gains occurred early in treatment and in each of the 10 sessions indicating that recovery is rapid and therefore optimal for a young population. An interesting finding is that treatment response is curvilinear; therefore, more research needs to be done to understand more about patterns of treatment response in psychotherapy. The majority of therapists in this study were given intensive, interactive training at the start of their employment, and weekly interactive TEAM-CBT training for a minimum of one year, with ongoing individual and group consultation/supervision. Future research should focus on well-designed trials to evaluate the effectiveness of this approach in other treatment settings, such as community mental health clinics, schools, college counseling centers, and hospital settings where brief or time-limited treatment is necessary. In addition, studies of baseline training requirements for clinical staff would need to precede replication studies. Finally, future studies could examine the impact of pre-treatment screening on outcomes.