Most American teens don't receive the appropriate amount of preventive health services, a new study finds. The University of California, San Francisco, researchers analyzed data gathered from almost 8,500 adolescents, ages 10 to 17, who took part in the Medical Expenditure Survey. The UCSF team focused on several aspects of preventive care for adolescents, including the extent to which they'd received care in the past year, whether they received counseling about various health issues, and whether they had any time alone with their healthcare provider.