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.