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The most common cause, he points out, is anxiety. A child who is worried about a problem at home or some other matter "can look hyperactive and distractible." Depression can also cause ADHD-like behavior. "A third cause is another form of neurological dysfunction, like a learning disorder," says Silver. "The child starts doodling because he didn't understand the teacher's instructions." All this is made more complicated by the fact that some kids -- and adults -- with ADHD also suffer from depression and other problems. To distinguish these symptoms from ADHD, doctors usually rely on interviews with parents and teachers, behavior-ratings scales and psychological tests, which can cost from $500 to $3,000, depending on the thoroughness of the testing. Insurance coverage is spotty.
Among the most important clues doctors look for is whether the child's problems can be linked to some specific experience or time or whether they have been present almost from birth. "You don't suddenly get ADD," says Wade Horn, a child psychologist and former executive director of CHADD. Taking a careful history is therefore vital.
For kids who are hyperactive, the pattern is unmistakable, says Dr. Bruce Roseman, a pediatric neurologist with several offices in the New York City area, who has ADHD himself. "You say to the mother, 'What kind of personality did the child have as a baby? Was he active, alert? Was he colicky?' She'll say, 'He wouldn't stop -- waaah, waaah, waaah!' You ask, 'When did he start to walk?' One mother said to me, 'Walk? My son didn't walk. He got his pilot's license at one year of age. His feet haven't touched the ground since.' You ask, 'Mrs. Smith, how about the terrible twos?' She'll start to cry, 'You mean the terrible twos, threes, fours, the awful fives, the horrendous sixes, the God-awful eights, the divorced nines, the I-want-to-die tens!' "
Diagnosing those with ADD without hyperactivity can be trickier. Such kids are often described as daydreamers, space cases. They are not disruptive or antsy. But, says Roseman, "they sit in front of a book and for 45 minutes, nothing happens." Many girls with ADD fit this model; they are often misunderstood or overlooked.
Christy Rade, who will be entering the ninth grade in West Des Moines, Iowa, is fairly typical. Before she was diagnosed with ADD in the third grade, Christy's teacher described her to her parents as a "dizzy blond and a space cadet." "Teachers used to get fed up with me," recalls Christy, who now takes Ritalin and gets some extra support from her teachers. "Everyone thought I was purposely not paying attention." According to her mother Julie Doy, people at Christy's school were familiar with hyperactivity but not ADD. "She didn't have behavior problems. She was the kind of kid who could fall through the cracks, and did."
Most experts say ADHD is a lifelong condition but by late adolescence many people can compensate for their impulsiveness and disorganization. They may channel hyperactivity into sports. In other cases, the symptoms still wreak havoc, says UCLA psychiatrist Walid Shekim. "Patients cannot settle on a career. They cannot keep a job. They procrastinate a lot. They are the kind of people who would tell their boss to take this job and shove it before they've found another job."