We study how the societal disruptions of the Covid-19 pandemic impacted diagnosis of a prevalent childhood mental health condition, Attention Deficit Hyperactivity Disorder (ADHD). Using both nationwide private health insurance claims and a state’s comprehensive electronic health records, we compare children exposed to the pandemic to same aged children prior to the pandemic. We find the pandemic reduced new ADHD diagnoses by 8.6% among boys and 11.0% among girls nationwide through February 2021. We further show that higher levels of in-person schooling in fall 2020 dampened the decline for girls but had no moderating effect for boys.