This year is the 40th anniversary of the passage of Public Law 94-142--most commonly known as the federal Individuals with Disabilities Education Act (IDEA). The law not only changed the way that students with disabilities are educated in this country, it also fundamentally changed the way that states fund their K-12 education programs. This ECS Progress of Education Reform outlines some of the facts--and myths--surrounding IDEA and how its passage has made state policymakers think differently about how they fund their public schools. Over the past 40 years, the federal IDEA law has changed the way states and school districts educate students with disabilities. Prior to 1975, the education that students with disabilities received varied greatly--with some students not being allowed to receive any form of public education. Since 1975 all students with disabilities are guaranteed an appropriate education in the least restrictive manner possible. The cost of implementing the IDEA mandates has fallen largely on state and local governments. With the federal government currently providing about one-third of the funds for special education that it committed to in the original legislation, state and local governments must think differently and refine their school-funding formulas.