Despite success of pharmacologic and psychosocial treatments, attention-deficit/hyperactivity disorder (ADHD) frequently results in significant personal impairment and socioeconomic burden. A challenge for the development of effective treatments targeting functional deficits in ADHD is the substantial heterogeneity in clinical features such as comorbidity, executive dysfunction, and cognitive disengagement. In this editorial perspective, we consider circadian dysfunction as a potentially critical mechanism underlying clinical heterogeneity and discuss current barriers to identifying and treating circadian dysfunction in pediatric ADHD. Recent advances in wearable sensors may offer new opportunities to elucidate the underlying role of circadian dysfunction in ADHD heterogeneity and support the development of personalized sleep treatments with the power to improve long-term educational, interpersonal, and occupational outcomes for children with ADHD.