62 Neurodevelopmental Disorders
Development and Course
Many parents first observe excessive motor activity when the child is a toddler, but symp-
toms are difficult to distinguish from highly  variable normative be haviors before age 4
years. ADHD is most often identified during elementary school years, and inattention be-
comes more prominent and impairing. The disord er is relatively stable through early ad-
olescence, but some individuals have a worsened course wi th development of antisocial
behaviors. In most individuals with ADHD , symptoms of motoric hyperactivity become
less obvious in adolescence and adulthood, bu t difficulties with restlessness, inattention,
poor planning, and impulsivity persist. A subs tantial proportion of children with ADHD
remain relatively impa ired into adulthood.
In preschool, the main manifestation is hyperactivity. Inattentio n becomes more prom-
inent during elementary school. During adoles cence, signs of hypera ctivity (e.g., running
and climbing) are less common and may be conf ined to fidgetiness or an inner feeling of
jitteriness, restlessness, or im patience. In adulthood, along wi th inattention and restless-
ness, impulsivity may remain problematic ev en when hyperactivity has diminished.
Risk and Prognostic Factors 
Temperamental. ADHD is associated with reduced be havioral inhibition, effortful con-
trol, or constraint; negative emotionality; an d/or elevated novelty seeking. These traits
may predispose some children to ADHD bu t are not specific to the disorder.
Environmental. Very low birth weight (less than 1,500 grams) conveys a two- to three-
fold risk for ADHD, but most children with low birth weig ht do not develop ADHD. Al-
though ADHD is correlated with smoking du ring pregnancy, some of this association