The U.S. Environmental Protection Agency (EPA) is ensuring that all new buses meet tighter standards developed to reduce diesel emissions and improve safety. Today's new buses are cleaner--60 times cleaner than buses built before 1990--and feature additional emergency exits, improved mirror systems, and pedestrian safety devices. But replacing America's school bus fleet will take time because diesel school buses can operate for 20 to 30 years. This paper describes Clean School Bus USA, a national, innovative program designed to help communities reduce emissions from diesel school buses. This program provides resources and assistance to fleet owners and operators as well as educators, transportation officials, and community partners committed to improving school bus fleets and protecting children's health. A case study of Pinellas County's adoption of the Clean School Bus USA program is presented.