Difficulties in reciprocal social interaction are hallmark features of several neuropsychiatric disorders, most notably autism spectrum disorder (ASD) and schizophrenia spectrum disorder (SSD). While recent studies have demonstrated substantial overlap in genetic etiology between ASD and SSD, little is known about common versus unique neural mechanisms that may underlie these downstream social deficits that cross diagnostic boundaries. Thus, a comprehensive imaging study examining social deficits in youth with ASD and adolescent- onset SSD at the neurochemical, connectivity, as well as functional activation level will be crucial in furthering our understanding of these underlying neural mechanisms. Specifically, the current project aims to examine how targeted social skills interventions may impact the organization of large-scale functional brain networks implicated in social cognition in these disorders, leading to improved outcomes. Thirty adolescents with ASD and 30 adolescents with SSD will undergo the Program for the Education and Enrichment of Relational Skills (PEERS), which is a 16-week parent-assisted social skills intervention that aims to improve friendship quality and social skills in teens with social difficulties. All participants will receive pre- and post-treatment MRI scans including functional MRI and magnetic resonance spectroscopy to quantify neural changes resulting from the intervention. All participants will also receive behavioral and social cognition assessments pre- and post-intervention to quantify real- world gains in social behaviors resulting from the intervention. Additionally, 30 typically developing adolescents will be recruited to serve as control participants and undergo two MRI and behavioral assessment sessions 16-weeks apart with no intervention in between. Specific aims include (1) examining inter-group disruptions in connectivity patterns, activation levels, and neurometabolite concentrations in key social brain regions pre-treatment in ASD and SSD groups, (2) examining inter-group changes in connectivity patterns, activation levels, and neurometabolite concentrations in key social brain regions in response to treatment in ASD and SSD groups, and, (3) dimensionally identifying intra-group differences in brain responses and how they relate to real-world treatment outcomes.