This article offers a socio-historical account of the development of the Attention Deficit/Hyperactivity Disorder (ADHD) diagnosis and methylphenidate treatment in America, attending particularly to the institutional and professional contexts that have supported this development. These historical developments frame a socio-cultural analysis that views contemporary schools and schooling practices as mediating factors in ADHD diagnoses and methylphenidate treatment. Consideration of the school as a mediating socio-cultural context illuminates important questions about the validity of the ADHD diagnosis, and about inter- and intra-national variations in the perception and tolerance of young children’s behavior, educational and behavioral goals for children, and styles of treating problem behaviors in children. It is argued that both local and cross-national research on schools and schooling are important means of increasing understanding of the complex socio-cultural factors inherent in the global growth of ADHD diagnoses and methylphenidate treatment.