Primer text from The College of William & Mary ADHD is one of the most commonly diagnosed conditions of children (Centers for Disease Control and Prevention, 2015). In a 2016 Centers for Disease Control and Prevention study, scientists found that 6.1 million children aged 2-17 years living in the U.S. had been diagnosed with attention-deficit/hyperactivity disorder (ADHD), which is similar to previous en Ages 6-11: Approximately 2.4 million children Ages 12-17: Approximately 3.3 million children