Children with comorbid autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) have significantly worse outcomes than those with either ASD alone or ADHD alone. Effective early treatments that account for ADHD symptoms have not been developed for young children with ASD. The overarching goals of this study are to (1) evaluate a novel early intervention that pharmacologically addresses ADHD symptoms prior to initiating early behavioral intervention, and (2) identify changes in behavioral and neurophysiological activity that may underlie improved outcomes in children with comorbid ASD and ADHD. The primary aim of this study is to evaluate whether a stimulant treatment augments efficacy of a novel, parent-delivered, behavioral intervention based on the Early Start Denver model (P-ESDM) through a 30 week, double-blind, placebo-controlled Phase II clinical trial. Secondary aims are to determine the efficacy of combined intervention in improving ADHD symptoms and the efficacy, safety, and tolerability of Adzenys-XR-ODT in young children with ASD+ADHD. The study will also examine correlations between behavioral changes and state-of-the-art eye-gaze tracking (EGT) and electroencephalographic (EEG) biomarkers to elucidate key ways in which ADHD impacts attentional and neural functioning in ASD+ADHD, and to potentially identify new targets for intervention in children with ASD+ADHD.