Journal of Consulting and Clinical Psychology, Vol 94(8), Aug 2026, 496-509; doi:10.1037/ccp0001026
Objective: Comorbidity of internalizing and externalizing problems is common in youths; transdiagnostic treatments were developed partly to address comorbidity. However, little is known about how outcomes of these treatments relate to comorbidity. We examined the association between internalizing-externalizing comorbidity and symptom outcomes for the transdiagnostic Modular Approach to Therapy for Children with Anxiety, Depression, Trauma, or Conduct Problems. Method: We analyzed data from three randomized controlled trials. Participants (N = 400) were sorted into four categories using baseline symptom severity cutoffs on the Youth Self-Report and Child Behavior Checklist: no clinical elevation, internalizing elevation only, externalizing elevation only, and comorbid internalizing/externalizing elevation. Nested multilevel models were used to test for moderation effects of clinical elevation over 18 months. Results: Youths and caregivers reported significant symptom decreases. No differences were found between caregiver-rated groups for Child Behavior Checklist total scores over time (ds = 0.03–0.09). However, youth reports showed the greatest reductions in Youth Self-Report total scores for those with youth-rated internalizing only (d = 0.20) and comorbid symptoms (d = 0.28) elevated at baseline as compared with no elevation. Results from youth reports suggested that older youths experience less symptom reduction. Conclusion: For caregiver reports, symptom reductions were similar across the four groups, suggesting that Modular Approach to Therapy for Children with Anxiety, Depression, Trauma, or Conduct Problems may be effective across problem areas. For youth reports, symptom reduction was more pronounced for the comorbid group and the internalizing only group as compared with no elevation. These findings support the appropriateness of Modular Approach to Therapy for Children with Anxiety, Depression, Trauma, or Conduct Problems in addressing comorbidity, but the effects of age and the contrast between caregiver and youth perspectives warrant further study. (PsycInfo Database Record (c) 2026 APA, all rights reserved)