1. Notwithstanding any provision of law to the contrary, any person duly certificated under the law governing the certification of teachers in Missouri who, after August 28, 1997, is first employed in a position which would otherwise qualify the person for membership in the public education employee retirement system pursuant to the provisions of sections 169.600 to 169.710 shall be a member of the public school retirement system pursuant to the provisions of sections 169.010 to 169.141, and shall receive creditable service on a pro rata basis in that system for subsequent certificated services which would otherwise have been creditable in the public education employee retirement system. Any such person shall have the option of being a member of the public education employee retirement system. The option election must be filed with the board of trustees of the public school retirement system within ninety days of first such employment following August 28, 1997.

2. Notwithstanding any provision of law to the contrary, any person duly certificated under the law governing the certification of teachers in Missouri who, on or after August 28, 2003, is employed by a public school, as defined in section 169.010, for at least seventeen but less than twenty hours per week on a regular basis shall be a member of the public school retirement system pursuant to the provisions of sections 169.010 to 169.141, and shall receive creditable service on a pro rata basis in that system. Any such person shall have the option of being a member of the public education employee retirement system. The option election must be filed with the board of trustees of the public school retirement system within ninety days of first such employment or within ninety days of August 28, 2003, whichever later occurs.

3. Any person who is a member of the public school retirement system or the public education employee retirement system pursuant to subsection 2 of this section may purchase credit in such system for service after August 28, 1991, that would have qualified such person for membership in either retirement system pursuant to subsection 2 of this section had such subsection been in effect prior to August 28, 2003; provided that such purchase of credit in the public school retirement system shall be subject to the provisions of section 169.056 and such purchase of credit in the public education employee retirement system shall be subject to the provisions of section 169.655.