40 ILCS 5/16-118

"Retirement": Entry upon a retirement annuity or receipt of a single-sum retirement benefit granted under this Article after termination of active service as a teacher. (a) An annuitant receiving a retirement annuity other than a disability retirement annuity may accept employment as a teacher from a school board or other employer specified in Section 16-106 without impairing retirement status, if that employment: (1) is not within the school year during which service was terminated; and (2) does not exceed the following: (i) before July 1, 2001, 100 paid days or 500 paid hours in any school year; (ii) during the period beginning July 1, 2001 through June 30, 2011, 120 paid days or 600 paid hours in each school year; (iii) during the period beginning July 1, 2011 through June 30, 2018, 100 paid days or 500 paid hours in each school year; (iv) beginning July 1, 2018 through June 30, 2026, 120 paid days or 600 paid hours in each school year, but not more than 100 paid days in the same classroom; (v) (blank); and (vi) beginning July 1, 2026, 100 paid days or 500 paid hours in each school year. Where such permitted employment is partly on a daily and partly on an hourly basis, a day shall be considered as 5 hours. (b) Subsection (a) does not apply to an annuitant who returns to teaching under the program established in Section 16-150.1, for the duration of his or her participation in that program.