In 1972 a congressional investigation was launched to determine the state of children with disabilities in the United States. The investigation determined that of 8 million children with disabilities, only 3.9 million of them were receiving an appropriate education. Thus, legislation was introduced in congress which guaranteed the right to education for all children.
Reference:
Wright P. and Wright P.D. (2021. October 18). The History of Special Education Law in the United States. Wrightslaw. https://www.wrightslaw.com/law/art/history.spec.ed.law.htm.