The U.S. DOE has responded to this question as follows:
"[The IDEA] authorizes the addition to the IEP team of other individuals at the discretion of the parent or the public agency only if those other individuals have knowledge or special expertise regarding the child. The determination of whether an attorney possesses knowledge or special expertise regarding the child would have to be made on a case-by-case basis by the parent or public agency inviting the attorney to be a member of the team.
The presence of the agency’s attorney could contribute to a potentially adversarial atmosphere at the meeting. The same is true with regard to the presence of an attorney accompanying the parents at the IEP meeting. Even if the attorney possessed knowledge or special expertise regarding the child, an attorney’s presence would have the potential for creating an adversarial atmosphere that would not necessarily be in the best interests of the child. Therefore, the attendance of attorneys at IEP meetings should be strongly discouraged."
64 Fed.Reg. 12478 (1999).