Trevor Reese, 13, gets his diphtheria, tetanus and pertussis booster shot from pediatric nurse practitioner Jenny Lu in Tustin, Calif., in August. Jae C. Hong/AP hide caption

itoggle caption Jae C. Hong/AP

Richard Meehan, 16, with his car at his home in Shelton, Conn in 2008. Researchers say tougher licensing laws have led to fewer fatal car crashes involving 16-year-old drivers. Bob Child/ASSOCIATED PRESS hide caption

itoggle caption Bob Child/ASSOCIATED PRESS