Who determines whether a students is "substantially limited"?

According to the federal regulations: “...placement decisions are to be made by a group of persons who are knowledgeable about the child, the meaning of the evaluation data, placement options, least restrictive environment requirements, and comparable facilities” [34 C.F.R. §104.35(c)(3)]. Unlike Special Education, the federal regulations for Section 504 do not require or even mention that parents are to be a part of the decision-making committee.