(A) a natural, adoptive or foster parent of the child (unless a foster parent is prohibited by State law from serving as a parent);20 U.S.C. section 1401(23)
(B) a guardian (but not the State if the child is a ward of the State);
(C) an individual acting in the place of a natural or adoptive parent (including a grandparent, stepparent, or other relative) with whom the child lives, or an individual who is legally responsible for the child's welfare; or
(D)  an individual assigned under either [section 1415(b)(2) or section 1439(a)(5)] to be a surrogate parent.
What happens when the parents are divorced?
If the parents of the child are divorced, both parents are considered a "parent" under the IDEA and have all of the parental rights established by the IDEA's procedural safeguards, unless a court order or state law specifies otherwise. The IDEA specifically allows for a judicial decree or court order to identify the person who is to act as the parent of the child and to make educational decisions on the part of the child. 34 C.F.R. section 300.30(b). If divorced parents both maintain shared legal and physical custody, each may be able to make educational decisions. If, however, a divorced parent does not have legal or physical custody, they may not be entitled to participate in the educational process. The siutation can be unclear in circumstances where parents share legal custody but not physical custody, or the other way around.
The best scenario would be for parents to ensure that the educational rights pertaining to the child are specified in a divorce agreement or addressed by the Court in its order.
What happens when the parents are unknown?
Section 1415(b)(2) includes a requirement that the local education agency establish procedures to protect the rights of the special education student "whenever the parents of the child are not known, the agency cannot after reasonable efforts locate the parents, or the child is a ward of the State." In these circumstances, the agency must assign a surrogate to act as the parent. School districts must establish a method for determining whether the child requires a surrogate and for assigning a surrogate parent. See 34 C.F.R. section 300.519. The surrogate cannot be an employee of the school district or any other agency involved in the education of the child, and must have "knowledge and skills that ensure adequate representation of the child."
Two circumstances are specifically addressed further: First, if the child is a ward of the State, the statute specifies that the surrogate may be appointed by the Judge overseeing the child's care. Second, if the child is an unaccompanied homeless youth, the school district is specifically responsible for appointing the surrogate. See 20 U.S.C. section 1415(b)(2).
Parents, including surrogate parents under the IDEA, or a divorced parent with legal and physical custody, have rights and responsibilities as determined by the procedural safeguards of the IDEA, and must be included and involved in all matters related to the identification, evaluation, placement and provision of FAPE to the child.