40 ILCS 5/8-108.3
An employee of the Board of Education of the city, regardless of his or her position, may establish up to 2 years of service credit in the Fund for part-time employment with the Board of Education of the city prior to becoming an employee by applying no later than 6 months after the effective date of this amendatory Act of the 103rd General Assembly and paying to the Fund for that employment an amount equal to the (1) employee contributions based on the actual compensation received and the rate of contribution in effect on the date of payment; plus (2) an amount representing employer contributions determined by the retirement board; plus (3) interest at the effective rate from the date of service to the date of payment. However, service credit shall not be granted under this Section for any such prior employment for which the applicant received credit under any other provision of this Code or during which the applicant was on a leave of absence.
40 ILCS 5/8-108.3