Perhaps the most debated warning sign is attention deficit, especially since critics charge that society is "medicalizing" normal fidgeting. To see how different ADHD brains are, researchers at the National Institute of Mental Health scanned the brains of 466 children with or without ADHD, and found that those with ADHD are not "a complete deviation from the template of typical development," as some studies suggested. Instead, ADHD brains are just slower to mature: there is about a three-year delay in the maturation of several cortical regions, especially those that control high-level thinking, attention and planning, and suppress inappropriate actions and thoughts. Despite press accounts—and even statements from NIMH—saying kids will grow out of ADHD, however, delayed maturation of the brain is not like taking longer to reach your adult height. "Teens with ADHD still have functional differences in their brain, areas of over- or underactivation," says NIMH's Philip Shaw. "The effects of the delay are carried forward."

It's not easy to tell if a red flag, be it failing to speak until the age of 2 or not smiling at 8 weeks, is truly cause for concern. But there is one unquestionably real consequence of thinking of your child as troubled, or slow, or difficult, or uninterested in school: it can subtly shift how you treat him and what you expect of him, turning harbingers into self-fulfilling prophecies.

© 2007