Mich. Comp. Laws § 38.1373
A member of this retirement system who enters active duty with the armed forces and within 24 months after the date of the member's honorable discharge or release from active duty from the armed forces resumes employment as a public school employee under this act, former Act No. 136 of the Public Acts of 1945, former Act No. 56 of the Public Acts of 1941, or former Act No. 184 of the Public Acts of 1937, shall receive not more than 6 years of service credit, except required service extending beyond 6 years, for time spent in the armed forces credited to the member as a member of the retirement system. Credit also shall be given to a member who meets the requirements of this section for active duty service which the member rendered before becoming a member, if the member pays to the retirement system an amount determined pursuant to section 74 for the years of service rendered before becoming a member which are to be credited. The total service credited under this section shall not exceed 6 years. Service shall not be credited if it is or would be credited under any other federal, state, or local publicly supported retirement system, but this restriction shall not apply to a person who has acquired or will acquire retirement eligibility under the federal government for services in the reserve. During the period of the service of a member, contributions to the reserve for employee contributions standing to the member's credit as of the last payroll date preceding military service shall be accumulated at regular interest.
MCL 38.1373