Symptom trajectories show that hyperactivity/impulsivity declines across childhood. At the group level, the course of inattention appears more variable. However, identification of subgroups of children showing stable, rising, and falling inattention over time is promising. Early ADHD-like symptoms portend risk for academic and social difficulties, as well as comorbid emotional and behavioral problems in childhood and adolescence. Several early risk factors appear to moderate these relations, including comorbid symptoms, parental psychopathology, socioeconomic disadvantage, and perhaps neuropsychological dysfunction. Furthermore, high levels of inattention and/or hyperactivity/impulsivity during the preschool period appear to compromise development of regulatory and neuropsychological functions, which in turn increases risk for negative outcomes later in childhood. Identified risk factors are targets for novel interventions, which ideally would be delivered early to at-risk children.