Parents, therapists and schools are struggling to figure out whether helping anxious teenagers means protecting them or pushing them to face their fears. Anxiety is the most common mental-health disorder in the United States, affecting nearly one-third of both adolescents and adults, according to the National Institute of Mental Health. But unlike depression, with which it routinely occurs, anxiety is often seen as a less serious problem. “Anxiety is easy to dismiss or overlook, partially because everyone has it to some degree,” explained Philip Kendall, director of the Child and Adolescent Anxiety Disorders Clinic at Temple University in Philadelphia.