Christina A. Samuels, writing for Education Week:
And then, there’s the money. Congress never funded the IDEA for the full amount that was authorized when the law was first signed. At that time, Congress estimated that it cost states twice as much to educate a student with disabilities as it does to educate a general education student, and the law authorizes the federal government to give up to 40 percent of that excess cost to states.
Congress has never come close to that mark; its $12.3 billion contribution in fiscal 2018 is more like 15 percent of the excess cost.
Those of use in special education as a profession cite this as a burden in conversation. New Jersey provides additional funding for special education but assumes that classified (eligible) students would never exceed about 14% of enrolled students. That’s just not true of so many districts.