34 CFR 300.9: Consent.

Consent means that—

(a) The parent has been fully informed of all information relevant to the activity for which consent is sought, in his or her native language, or through another mode of communication;

(b) The parent understands and agrees in writing to the carrying out of the activity for which his or her consent is sought, and the consent describes that activity and lists the records (if any) that will be released and to whom; and

(c)(1) The parent understands that the granting of consent is voluntary on the part of the parent and may be revoked at any time.

(2) If a parent revokes consent, that revocation is not retroactive (i.e., it does not negate an action that has occurred after the consent was given and before the consent was revoked).

(3) If the parent revokes consent in writing for their child's receipt of special education services after the child is initially provided special education and related services, the public agency is not required to amend the child's education records to remove any references to the child's receipt of special education and related services because of the revocation of consent.