Which court case established the right for all children with mental retardation to a free public education?

The correct choice is B, as the case of Penn Association for Retarded Citizens v. Commonwealth of Pennsylvania played a pivotal role in establishing the right to a free public education for children with mental retardation. This landmark decision, issued in 1971, determined that it was unconstitutional for the state to deny children with mental retardation access to public education, reinforcing the principle that all children, regardless of their disabilities, have the right to receive an appropriate education. This case laid the groundwork for subsequent federal legislation, including the Education for All Handicapped Children Act, now known as the Individuals with Disabilities Education Act (IDEA), which further developed educational rights for students with disabilities.

Other cases listed, such as Plyler v. Doe and Brown v. Board of Education, address different issues related to education and civil rights but do not specifically focus on the rights of children with disabilities. Endrew F. v. Douglas County School District is significant as it clarified the standards for educational benefits under IDEA, but it did not establish the right to education for children with mental retardation, which was firmly laid down in the earlier case mentioned.