The Summer Treatment Program (STP) is an effective psychosocial intervention for children with attention-deficit/hyperactivity disorder (ADHD) and provides a context to enhance children’s strengths. Most evaluations, however, have focused on reducing primary ADHD symptoms rather than enhancing strengths. Additionally, minimal research has explored mechanisms of change contributing to strength-based outcomes within the STP. The Building Relationships and Targeting Healthy Emotions (BREATHE) program is an adapted, 8-week long STP. Participants engaged in social skills training and recreational activities, and their parents concurrently participated in weekly training workshops. The purpose of this study was to examine children’s treatment outcomes related to strength-based adaptive functioning and understand the role of positive and negative affect as mechanisms of change. Results revealed that participating children (N = 14) demonstrated statistically and clinically significant improvements in their overall behavioral and emotional strengths. Additionally, outcomes were influenced by various modes of affect and prosocial behaviors: Positive affect at baseline was associated with improvements in overall strengths, whereas decreases in negative affect from pre- to midtreatment were associated with improvements in social functioning from mid- to posttreatment. Likewise, gains in children’s prosocial behavior as measured by point sheet data from pre- to midtreatment were associated with gains in prosocial behavior as reported by parents from mid- to posttreatment. Although the current study is limited in sample size, results suggest the potential for the BREATHE program to improve children’s behavioral and emotional strengths and identify potential mechanisms of change for future study of strength-based outcomes.