What Is ADHD?

Andrew Scott had always been an active child. From the time he learned to walk his parents noticed he was "into everything." Andrew's preschool teachers frequently commented on how active he was, and his kindergarten teacher observed that he was "quite a handful." First grade passed without any major problems, though his level of activity seemed to overwhelm some of the other children during playtime. In third grade, however, Andrew began to fall behind in math and reading. His teacher said he was too restless. During class he bothered the children around him. He seemed unable to focus on a learning activity for longer than a few minutes. On the playground he was "over-physical" with his peers, invading their space and then overreacting when they pushed him away.

Around the middle of the year, Andrew's teacher met with his parents. His teacher told them that Andrew's problems paying attention, his high activity level, and troubles with schoolwork may indicate the presence of attention-deficit/hyperactivity disorder (ADHD). She explained that ADHD often goes undetected until children enter school and academics and social relationships begin to be affected.

Despite the teacher's positive attitude, Andrew's parents were stunned by her recommendation that their son be evaluated for the causes of this behavior. They had always been challenged by their active child, but they had never considered his behavior out of the ordinary for a healthy young boy. As Andrew's father often pointed out, Andrew was "just like me when I was in school" — eager, excited, and always on the go. While both parents agreed that Andrew could use some extra help with his social skills and reading, they did not see how these behaviors could be thought of as a medical condition. "I think his teacher just can't handle him in class," Andrew's mother told her husband later when they were back at home. "She has a discipline problem and she calls it ADHD. I think it's the school that should be evaluated."

The Keller family was experiencing similar confusion. Their 12-year-old daughter, Emma, was also having problems. However, she was on the quiet and somewhat anxious side. Since early childhood, she had been a "dreamer" whose thoughts tended to drift easily. She often forgot things she had recently learned or been told and spent much of her time alone. In recent years, her "randomness" and lack of organization had begun to seriously affect her school performance, social life, and family relationships. She was having trouble completing tasks and was messy and careless about her schoolwork. Her parents noted that she was often forgetful or spacey. At times it seemed as if her mind was elsewhere and that she was not listening. Still, Emma's parents felt that her behavior was typical of many girls her age and was nothing that a little maturation and help with organization could not cure. Was it really necessary, they asked Emma's pediatrician, to consider this a medical issue or to start an evaluation?

As different as Andrew's and Emma's situations seem to be, both are typical for children with ADHD. Attention-deficit/hyperactivity disorder limits children's ability to filter out unimportant input, focus, organize, prioritize, delay gratification, think before they act, or perform other activities called executive functions that most of us perform automatically. In children such as Andrew, with hyperactive-impulsive elements to his ADHD, the disorder presents itself as his not being able to control impulses or regulate activity levels, even when he knows how he is expected to behave. In those with inattentive-type ADHD, including Emma, not being able to filter information means that someone walking by the classroom can claim as much attention as the teacher's lecture, and that a date with a friend can be forgotten in a flood of unsorted information.

These behaviors — short attention span, forgetfulness, not being able to sit still, unusually high activity level, and a tendency to act before thinking — are common in children. Families are often surprised when their child is referred for an evaluation. Adding to their confusion is the fact that these behaviors are present but to a lesser degree in all children and adolescents, although those with ADHD exhibit more extreme and immature forms of these behaviors. Many school systems will not allow teachers to describe their concerns as "perhaps ADHD" because they feel this is a diagnosis to be made by a physician or a psychologist. Instead they will describe the behaviors that a child is showing that are interfering with his learning.

These behaviors interfere in significant ways with children's day-to-day functioning, and they do not outgrow them at the same pace that other children do. Because other disorders, such as learning disabilities, oppositional defiant disorder, autism spectrum disorder, obsessive-compulsive disorder, anxiety, and depression can resemble ADHD (and, in fact, often accompany it), it can be difficult to tell whether a child has another condition, ADHD, or both. Finally, the fact that ADHD is diagnosed through careful observations of inattentive, hyperactive, and impulsive behaviors across the major settings of a child's life — rather than with laboratory tests used to diagnose such disorders as type 1 diabetes — leads some adults and the popular press to question whether ADHD exists at all.

Yet a large body of convincing evidence suggests that ADHD is a biological, brain-based condition. The scientific research on ADHD is more thorough and compelling than for most behavioral and mental health disorders, and even many medical conditions. Even so, among many parents, it remains controversial and misunderstood. As early as 1998 the National Institutes of Health, responding to public concern and debate about ADHD diagnosis and treatment, assembled a group of experts for a consensus conference on ADHD. These experts published their conclusions stating that ADHD is indeed a medical disorder.

Attention-deficit/hyperactivity disorder is among the most prevalent chronic childhood disorders, second only to asthma. National survey data from 2016 show 9.4% of US children have been diagnosed with ADHD. The Centers for Disease Control and Prevention has reported that about 4.5 million children (ages 3–17 years) in the United States have ADHD, and the condition currently accounts for as many as 30% to 50% of child referrals to mental health services. Many people believe that the prevalence of ADHD has increased significantly in recent decades, perhaps due to environmental factors, but...