Mont. Code Ann. § 20-5-108

It shall be the duty of the trustees of any district where an Indian child resides to require the child to attend school in the same manner as any other child residing in the district, unless it is prohibited by the laws or treaties affecting the Indian tribe of which such child is a member or the Indian reservation on which such child resides. When such a prohibition exists, the trustees of any district shall have the authority to accept from the tribal council or other governing body of the Indian tribe or the Indian reservation authorization to enforce the compulsory attendance provisions of this title and compel the school attendance of the Indian children belonging to the tribe or residing on the reservation.