Attention-Deficit/Hyperactivity Disorder (ADHD) is the most commonly occurring neurodevelopmental disorder in the United States, with current prevalence rates between 8% and 11%, up from an estimated 5% in 2003. Despite decades of research, individuals with ADHD continue to be at significantly greater risk for poor life outcomes compared to non-affect peers. Evidence-based interventions for ADHD include stimulant medications and psychosocial treatments, but these practices are not always feasible or acceptable due to adverse side-effects, cost, availability, and poor treatment adherence. ADHD is considered to be a result of a physiological disruption of select catecholaminergic systems (e.g. dopamine and norepinephrine) and related under-arousal of cognitive functions of the pre-frontal cortex involved in executive functioning (EF). Research indicates that AAI with dogs is effective for improving social-behavioral outcomes related to EF deficits. The mechanisms by which AAI improves outcomes for this group and mediators of these outcomes, however, is not yet understood. These gaps in understanding hinder progress in the application of AAI, limiting the acceptability and availability of this integrative health care practice. Recent research in other populations suggests that AAI acts on hypothalamic-pituitary-adrenal (HPA) axis activity, reducing physiological stress Children with ADHD, however, present with different Autonomic Nervous System (ANS) response patterns when compared to typically developing children and children with other mental health disorders and this phenomenon points to altered physiological activity in response to stress, social feedback, and emotional stimuli when compared to their peers. The bio-social mechanistic hypothesis proposed in this study contends that dogs may elicit physiological responses related to cognitive arousal of EF systems, thereby enhancing response to treatment in children with ADHD. Furthermore, given the heterogeneity of impairment and high comorbidity with other mental health disorders among children with ADHD and the prevalence of ADHD across cultures, race and ethnicity, individual differences in response to AAI and in child/animal interaction may potentially mediate response to AAI. This research will explore these gaps by: 1) replicating findings from a previous AAI RCT on social-behavioral outcomes, 2) exploring candidate physiological responses to AAI over time, and 3) ascertaining if individual differences during AAI mediate primary and/or exploratory main outcomes. This study hypothesizes AAI will result in enhanced social-behavioral outcomes and improved diurnal patterns of HPA and ANS for these children. Furthermore, it is suspected acute physiological responses to AAI (markers of HPA \& ANS) and social interaction quality (child/child and child/dog) will mediate main outcomes. To explore these hypotheses, the investigators will conduct an exploratory parallel-group randomized controlled clinical trial with 48 young children with ADHD, participating in psychosocial intervention with or without AAI using a previously manualized AAI model developed and found successful in prior work. This work will yield the first information on candidate mechanisms thought to play an important role in AAI for children with ADHD, thus laying foundations for later submission of a fully powered, multi-site randomized clinical trial aimed to better inform approaches refined for this group, and promote acceptability and generalizability of AAI with children with special needs.