It is estimated that between three and five percent of children--or approximately two million children in the United States--have attention deficit hyperactivity disorder (ADHD). This means that in a classroom of 25 to 20 students, it is likely that at least one will have ADHD.
Those statistics come from the National Institute for Mental Health (NIMH), which also points out that while a child with ADHD faces a difficult task in achieving his or her full potential, the task is not insurmountable. Since ADHD often continues into adulthood, it is important to help children learn to deal with it early on, and that takes teamwork from parents, guidance counselors, teachers and school administration.
According to the NIMH, it is the school's obligation to evaluate children it suspects may have ADHD. The diagnosis is becoming more common, however, and children may come into the classroom having already received treatment such as behavior modification and medication--as well as an Individualized Educational Plan (IEP).