Tennessee Code Title 49. Education § 49-3-312

(a) A substitute teacher substituting for a regular teacher on leave authorized for a period not exceeding twenty (20) consecutive teaching days is not required to possess a teacher's license.

(b) A substitute teacher who is a retired teacher is not required to continue to renew the teacher's license in order to work as a substitute teacher. The rate of compensation for a retired teacher without an active teaching license must not be less than the rate of compensation set by the LEA for a retired teacher with an active teaching license. This subsection (b) only applies to retired teachers who retired after July 1, 2011 through July 1, 2016.