34 C.F.R. §300.345.  Parent participation.

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(d) Conducting an IEP meeting without a parent in attendance. A meeting may be conducted without a parent in attendance if the public agency is unable to convince the parents that they should attend. In this case the public agency must have a record of its attempts to arrange a mutually agreed on time and place, such as--

(1) Detailed records of telephone calls made or attempted and the results of those calls;
(2) Copies of correspondence sent to the parents and any responses received; and
(3) Detailed records of visits made to the parent's home or place of employment and the results of those visits.