Tenn. Code § 49-1510
Teachers in the service of an employer operating a local retirement fund or plan or arrangement containing provisions for the retirement of teachers on a joint contributory basis who are eligible for membership therein shall not be members of the retirement system established under this chapter, and such teachers shall make no contributions to this retirement system nor be eligible for benefits under this retirement system except as provided in § 49-1542. Members of this system who are eligible to belong to the county officials' retirement system may elect to join such system and withdraw the membership and contributions from this system; any person making such an election shall make no further contributions to this system nor be eligible for retirement benefits under the provisions of this system.
T.C.A. § 49-1510