Who counts as a parent with the ability to enforce or challenge an IEP under the IDEIA?

In a day and age where divorce rates near 50% issues involving which parent and who can enforce or litigate the appropriateness of an IEP are hitting the courts more and more often. Often when parents get divorced they have joint custody for purposes of decision making with one parent having primary physical custody. However, in more and more cases, the decision making ability when it comes to education or health decisions is being vested in one parent rather than both. In a recent case Fuentes v. Board of Education, City of New York, et al., F.3d (2nd Circuit, August 26, 2008) the Court found in line with other decisions that IDEA's allowance of the parent or guardian rights to bring an action will not apply where the “biological or adoptive parent does not have legal authority to make educational decisions for the child.”