The biggest breakthrough came in 1971. Attorney Thomas K. Gilhool represented the Pennsylvania Association for Retarded Citizens v. Commonwealth of Pennsylvania (PARC v. Commonwealth) in a case that resulted in a landmark decision. The court affirmed the right to education at public expense and due process for children with disabilities. Gilhool used Brown v. Board of Education in his arguments. Twenty-seven federal court cases followed and led to the birth of P. L. 94-142, the law that mandated that right.
PARC v Commonwealth was restricted to all "children with mental retardation." In the same year, Mills v Board of Education of District of Columbia affirmed the Pennsylvania decision and expanded its application to all children with disabilities.
The Right to Education Based on Brown v. Board of Education
The court decisions did not use "least restrictive environment," but certainly described it. The Pennsylvania settlement said:
Placement in a regular school is preferable to placement in a special school class is preferable to placement in any other type of program of education and training.
The court cases of the early 1970s that focused on institutions did use "least restrictive environment" explicitly.
Following on the court decisions, a number of federal laws between 1973 and 1975 strengthened the civil rights protections related to education.