Actually, no, IDEA only dates from 1990 I believe. The court cases go back to PARC v. Pennsylvania and Mills v. D.C. Board of Education in the early 1970s.
The first law with the IDEA title was passed in 1975 and was amended in 1990 and 1997. The early 1970s cases were interpreting ESEA, a forerunner of the IDEA that provided for "equal access to education" dating to 1965. In 1970, ESEA was amended to expressly cover the handicapped.