Mo. Rev. Stat. § 169.595
Any employee of a school district who is a member of a system pursuant to the provisions of this chapter shall remain a member of such system during any period of leave under sick leave provisions of the district or under workers' compensation and shall receive creditable service credit, not otherwise allowable, for such leave time if the employee makes contributions to the system equal to the amount of contributions which would have been made by such employee if such employee had been on active service status, in accordance with rules and regulations established by the respective retirement system. The school district shall make contributions on behalf of the employee as provided in the applicable provisions of this chapter relating to the system involved. The contributions of the member shall be made on a monthly or other basis in the manner provided by the system. The creditable service credit provided in this section shall be granted only for the actual time of the period of leave under sick leave provisions of the district or under workers' compensation and shall not be granted after the date the member begins receiving retirement benefits from the system in which the person is a member.
§ 169.595, RSMo