40 ILCS 5/15-113.6
"Service for employment in public schools": Includes those periods not exceeding the lesser of 10 years or 2/3 of the service granted under other Sections of this Article dealing with service credit, during which a person who entered the system after September 1, 1974 was employed full time by a public common school, public college and public university, or by an agency or instrumentality of any of the foregoing, of any state, territory, dependency or possession of the United States of America, including the Philippine Islands, or a school operated by or under the auspices of any agency or department of any other state, if the person (1) cannot qualify for a retirement pension or other benefit based upon employer contributions from another retirement system, exclusive of federal social security, based in whole or in part upon this employment, and (2) pays the lesser of (A) an amount equal to 8% of his or her annual basic compensation on the date of becoming a participating employee subsequent to this service multiplied by the number of years of such service, together with compound interest from the date participation begins to the date payment is received by the board at the rate of 6% per annum through August 31, 1982, and at the effective rates after that date, and (B) 50% of the actuarial value of the increase in the retirement annuity provided by this service, and (3) contributes for at least 5 years subsequent to this employment to one or more of the following systems: the State Universities Retirement System, the Teachers' Retirement System of the State of Illinois, and the Public School Teachers' Pension and Retirement Fund of Chicago.
The service granted under this Section shall not be considered in determining whether the person has the minimum of 8 years of service required to qualify for a retirement annuity at age 55 or the 5 years of service required to qualify for a retirement annuity at age 62 or the 10 years of service required to qualify for a retirement annuity at age 67, as provided in Section 15-135. The maximum allowable service of 10 years for this governmental employment shall be reduced by the service credit which is validated under paragraph (2) of subsection (b) of Section 16-127 and paragraph 1 of Section 17-133.
40 ILCS 5/15-113.6