In 1998, the National Institutes of Mental Health agreed that attention-deficit hyperactivity disorder (ADHD) is indeed a legitimate psychologic condition even though its definition has not been fully pinned down. ADHD is a syndrome generally characterized by the following symptoms that first occur before the age of seven:
Inattention, Distractibility, Impulsivity, Hyperactivity.

Some experts further categorize ADHD into three subtypes:
Behavior marked by hyperactivity and impulsivity, but not inattentiveness.
Behavior that is marked by inattentiveness, but not hyperactivity and impulsivity.
A mixed type.
There are some issues with these criteria, and arguments exist for both an over- and underdiagnosis of this problem.

Defining ADHD is made particularly difficult because one-third of the cases are accompanied by learning disabilities and other neurologic or emotional problems. It is likely that the term attention-deficit hyperactivity disorder will eventually give way to subgroups of problems that include some of these general symptoms. For more details, see How is Attention-Deficit Hyperactivity Diagnosed? below.
General Description of a Child with ADHD
Studies now indicate that ADHD can be diagnosed in children by age four. Parents may notice symptoms even earlier. (One mother reported that three days after delivery, nurses were referring to her ADHD son as "Wild Willie.

") The classic ADHD symptoms, inattention, distractibility, impulsivity, and hyperactivity often do not adequately describe the child's behavior, nor do they describe what is actually happening in the child's mind. Other behaviors also often coincide with the classic symptoms.
Some experts are focusing on deficits in so-called "executive functions" in the brain as the key to understanding all ADHD behaviors. Such impaired executive functions may include the following:
Inability to hold information in short-term memory.
Impaired organization and planning skills.

Difficulty in establishing and using these goals to guide behavior, such as selecting strategies and monitoring tasks.
Inability to keep emotions from becoming overpowering.
Inability to shift efficiently from one mental activity to another.
Hyperactivity. The term hyperactive is often confusing for those who expect to observe a child racing unceasingly about. A boy with ADHD playing a game, for instance, may have the same level of activity as the other children without the syndrome.

If a high demand is placed on the ADHD child's attention, however, then his motor activity intensifies beyond the levels of the other children. In a busy environment, such as a classroom or a crowded store, for example, ADHD children often become distracted and react by pulling items off the shelves, hitting people, or spinning out of control into erratic, silly, or strange behavior.
Impulsivity and Temper Explosions. Even before the "terrible two's," impulsive behavior is often apparent; the toddler may gleefully exhibit erratic and aggressive gestures, such as hair pulling, pinching, and hitting. Temper tantrums, normal in children after two, are usually exaggerated and not necessarily linked to a specific negative event in the life of an ADHD child.

One of the most painful events a parent may experience is an abrupt and aggressive attack that may occur after cuddling a young ADHD child. Often this reaction seems to be caused not by anger, but by the child's apparent inability to endure overstimulation or displays of physical affection.
Attention and Concentration. ADHD children are usually distracted and made inattentive by an overstimulating environment (such as a large classroom). They are also inattentive when a situation is low-key or dull.

Some experts believe that certain parts of the brain in ADHD children may be underactive so that they fail to be aroused by nonstimulating activities. In contrast, however, they may exhibit a kind of "super concentration" to a highly stimulating activity (such as a video game or a highly specific interest). Such children may even become over-attentive, so absorbed in a project that they cannot modify or change the direction of their attention.
Impaired Short-Term Memory. Many experts now believe that an essential feature in ADHD, as well as in learning disabilities, is impaired working, or short-term, memory. People with ADHD are unable to "hold" groups of sentences and images in their mind until they can extract organized thoughts from them.

Such people then may not necessarily be inattentive so much as be unable to remember a full explanation (such as a homework assignment) or unable to complete processes that require remembering sequences, such as model building. In general, children with ADHD are often attracted to activities (e.g. television, computer games, or active individual sports) that do not tax this working memory or produce distractions. Children with ADHD have no differences in long-term memory compared with other children.
Inability to Manage Time.

Studies suggest that children with ADHD have difficulties being on time and planning the correct amount of time to complete tasks. (This may coincide with short-term memory problems.) In one study, although children with probable ADHD were able to self-report many ADHD symptoms, they tended to believe they used their time wisely, in contrast to reports by their teacher.
Lack of Adaptability.

ADHD children have a very difficult time adapting to even minor changes in routines, such as getting up in the morning, putting on shoes, eating new foods, or going to bed. Any shift in a situation can precipitate a strong and noisy negative response. Even when they are in a good mood, they may suddenly shift into a tantrum if they meet with an unexpected change or frustration. In one experiment, ADHD children were able to closely anchor their attention when they were directly cued to a specific location, but they had difficulty shifting their attention to an alternative location.
Hypersensitivity and Sleep Problems.

ADHD children are often hypersensitive to sights, sounds and touch, and complain excessively about stimuli that seem low key or bland to others. Sleeping problems usually occur well after the point at which most small children sleep through the night. In one study, 63% of children with ADHD had trouble sleeping.