Mich. Comp. Laws § 380.966
If territory is attached to a school district effective before September 1 of a year, school operational millage for that year shall be levied on property in the territory by the attaching school district. If territory is attached to a school district effective on or after September 1 of a year, school operational millage for that year shall be levied on property in the territory by the school district from which the territory is detached. The school officials of the district entitled to levy school operational millage upon the transferred territory shall certify the school operational millage, and the territory over which it is to be spread, to the proper taxing officials when certifying the taxes to be levied by the school district.
MCL 380.966