Ill. Admin. Code tit. 80, § 1650.340
a) Granting Out-of-System Service
1) For purposes of granting out-of-system service as provided in Section 16-127(b)(2) of the Code, once the statutory minimum service requirement has been met, the member may purchase the portion of out-of-system service available at the time of purchase based on total creditable service years, provided one of the following conditions are met:
b) For purposes of granting service credit for an approved leave of absence as provided in Section 16-127(b)(5)(i) of the Code, the statutory return-to-teaching requirement is met when the member returns to teaching service creditable under this System or the State Universities Retirement System for the period of the leave or one year, whichever is less. A leave of absence is creditable as an approved leave if:
2) The employer promised renewed employment at the end of the leave; and
(Source: Amended at 44 Ill. Reg. 7905, effective April 24, 2020)