Attention deficit hyperactivity disorder (ADHD) is very common. It's the most common behavior problem diagnosed among school -age children in the United States. ^{1 2}

But it's hard to say exactly how many children have ADHD because the condition is difficult to spot.³ Also, one doctor may say a child has ADHD while another may not. So if we compare studies, the number of children said to have ADHD can be very different.

What we do know is that more children are being diagnosed with ADHD as more people get to know about it. Parents are now more likely to take their child to a doctor if he or she has behavior problems. Schools, too, are more aware of ADHD and better prepared to give you information about how your child behaves in class.

Here's what we know from the research.

• It's estimated that 3 percent to 7 percent of school-age children in the United States have ADHD. That's around 2 million children.^{4 5 6}This means that, in an average class of 30 children, there may be at least one or two children with ADHD.^{5 6}
• Boys seem to be more likely to have ADHD than girls. In the United States, two to three boys are diagnosed with the condition for every girl who's diagnosed with it.⁶ But this may be because boys and girls tend to have different symptoms.
• Inatte ntion is more common among girls, while hyperactivity is more common among boys. And a boy who is hyperactive (shouting, running about and getting into trouble) is more noticeable than a girl who is inattentive (daydreaming, forgetful and easily distracted). To learn more, see What are the symptoms of ADHD?
• Children who are whi te are more likely to be diagnosed with ADHD than children who are black or Hispanic. ⁶ But it is difficult to say whether white children are actually at greater risk of getting ADHD. It may be simply that they have better access to health services, so they are more likely to be diagnosed.