ADHD, or Attention Deficit Hyperactivity Disorder (formerly known as ADD) is a neurological condition that causes children to lose focus and behave in ways that, if untreated, may make it difficult for them to successfully participate in school, social and family life. Children with ADHD can be inattentive, hyperactive or impulsive, and many have a combination of these behaviors. Other learning disabilities or mental conditions can also accompany ADHD.

Although it's the nation's most common childhood mental disorder -- 8 percent of all U.S. kids, which translates to about 5 million, have been diagnosed -- ADHD can be surprisingly hard to spot because it affects individual children so differently. ADHD kids can be rowdy troublemakers who get into fights and fail at school, excessively chatty straight-A know-it-alls who constantly interrupt their teachers, or "space cadets" who stare out the window unaware that rest of the class has left for lunch. While all young children can be impulsive, hyperactive or inattentive at times, for children with ADHD these behaviors are so frequent and severe that they interfere with normal activities, often leaving them confused, frustrated, or angry.

According to the Centers for Disease Control and Prevention, boys are more likely to be diagnosed with ADHD than girls (9.5 percent of all boys, versus 5.9 percent of girls) but experts are unsure if that means more boys actually have the condition, or if they're just more likely to have the type of ADHD that results in disruptive behavior. Kids who act out, especially in school, are more likely to be noticed and referred for diagnosis than those who drift off into their own world.

The good news is that a great deal of research has been done on ADHD (which has been a recognized mental condition since the 1960s) and there are a number of strategies, including medication, behavioral modification and school accommodations, that can help children manage their condition and lead successful, happy lives.