(1) Except for any period prior to the member’s employment in an eligible position, a plan 2 or plan 3 member who is employed by a school district or districts or an educational service district:

(a) Shall receive a service credit month for each month of the period from September through August of the following year if he or she is employed in an eligible position, earns compensation earnable for eight hundred ten hours or more during that period, and is employed during nine months of that period;

(b) Who earns earnable compensation in an eligible position during the period from September through August, except under (a) of this subsection, shall receive service credit according to one of the following methods, whichever provides the most service credit to the member:

(i) If a member in an eligible position for each month of the period from September through August of the following year does not meet the hours requirements of (a) of this subsection, the member is entitled to one-half service credit month for each month of the period if he or she earns earnable compensation for at least six hundred thirty hours but less than eight hundred ten hours during that period, and is employed nine months of that period;

(ii) A member employed in an eligible position for at least five months of a six-month period between September through August of the following year who earns earnable compensation for six hundred thirty or more hours within the six-month period will receive a maximum of six service credit months for the school year, recorded as one service credit month for each month of the six-month period;

(iii) In all other instances, a member in an eligible position is entitled to service credit months as follows:

(A) One service credit month for each month in which compensation is earned for ninety or more hours;

(B) One-half service credit month for each month in which compensation is earned for at least seventy hours but less than ninety hours; and

(C) One-quarter service credit month for each month in which compensation is earned for less than seventy hours.

(2) The department shall adopt rules implementing this section.