Background: Children with autism spectrum disorders (ASD) often carry co-morbid diagnoses and present with impairing heterogeneous symptomatology (Leyfer et al. in "J Autism Dev Disord" 36(7): 849-861, 2006. doi:10.1007/s10803-006-0123-0). However, research from controlled laboratory settings often fails to examine the vast number of co-occurring clinical challenges that are seen in youth with ASD treated in "real-world" clinical service settings (Ehrenreich-May et al. in "Adm Policy Ment Health" 38(5): 398-411, 2011. doi:10.1007/s10488-010-0328-6). Objective: This study aimed to better understand this heterogeneity in children with ASD receiving services in clinical service settings and to assess the effectiveness of a group therapy intervention targeting these symptoms. Methods: Thirty-nine children with ASD were treated in a large private practice with the Resilience Builder Program® (RBP). Pre- and post-treatment questionnaires assessing social, emotional and behavioral functioning were collected. Results: Youth with ASD showed clinically elevated or at-risk pre-treatment levels of multiple behavioral and emotional symptoms. Children showed improvements in emotional control as well as a reduction in aggression and autistic symptomatology following treatment. Conclusions: This study highlights the importance of understanding heterogeneity in ASD and indicates that the RBP is a promising intervention to improve overall emotional and behavioral functioning in children with ASD in a clinical service environment.