On payment at the rates prescribed herein on the date of appointment or employment as teachers, or as such rates are adjusted by the Board of Education, but not less than $450 per year of service, members shall be entitled to have credited for pension purposes service as: (a) a civil service librarian in the public schools of the city, or in such city; (b) a playground or recreational instructor for such city or the Park District in such city; (c) a school clerk, employed by the Board of Education; and (d) a lunchroom manager for the Board of Education. Interest on such payments shall be charged commencing one year after the date of such appointment or employment.
     Effective September 1, 1974, the interest rate to be charged by the Fund shall be 5% per annum compounded annually.