Missouri Revised Statutes Title XI. Education and Libraries § 169.055. Purchase of equivalent service, leave of absence--part-time teachers may receive creditable service, when

1. A member who is assigned to a leave of absence by the member's employer, with compensation provided in the contract of employment for the leave period to be not less than fifty percent of the amount which would have been paid had the member not been on leave, may acquire creditable service for the period of leave. A member may elect to receive credit for the time spent on leave of absence at the time of the leave of absence and shall retain continued membership in the system during the leave period provided the full contributions are withheld and remitted on the basis of the compensation which would have been received if the member had not been on leave of absence and the employer's matching amount is remitted on the basis of the same amount of compensation which would have been paid if the member had not been on leave of absence.

2. Notwithstanding any provision of this chapter to the contrary, any person employed as of August 28, 1993, by the department of elementary and secondary education whose employment is covered by the retirement system provided by sections 169.010 to 169.141, and who without terminating that employment subsequently becomes a part-time employee of that department in a position requiring services for at least twenty hours per week on a regular basis, may elect within ninety days of August 28, 1993, or within ninety days of the date upon which the part-time employment begins, whichever is later, to be covered by that retirement system and shall receive pro rata creditable service with that retirement system for such part-time employment. Credit shall not be allowable in both that retirement system and another Missouri public retirement system for such employment.