Global Autism Assistance Act of 2008 - Directs the Administrator for the United States Agency for International Development (USAID) to establish and administer a health and education grant program (Global Autism Assistance Program) to: (1) support activities by nongovernmental organizations and other service providers, including advocacy groups, focused on autism in developing countries; and (2) establish a "teach the teachers" program to train health and education professionals working with autistic children in developing countries.