Mich. Comp. Laws § 38.92
If a teacher on continuing tenure is employed by another controlling board, the teacher is not subject to another probationary period of more than 2 years beginning with the date of employment, and may at the option of the controlling board be placed immediately on continuing tenure. A notice provided under section 3 of article 2 shall be given not later than 60 days before the completion of the probationary period. If a teacher on continuing tenure becomes an employee of another controlling board as a result of school district annexation, consolidation or other form of school district reorganization, the teacher shall be placed on continuing tenure within 30 days unless the controlling board, by a 2/3 vote on an individual basis, places the teacher on not more than 2 years' probation. However, if such a teacher is under contract but not on continuing tenure with the employing board as of the effective date of the amendatory act that added this sentence, the teacher is not subject to another probationary period of more than 1 year beginning with the date of employment.
MCL 38.92