R.I. Gen. Laws § 16-16-6

In determining the creditable service of any teacher employed in any city or town for the purposes of retirement there may be added to, and included in, total service as defined in this chapter not more than five (5) years of service as a teacher or in a capacity essentially similar or equivalent to that of a teacher in any private school or institution, in any charter school not subject to subdivision 16-77-4(b)(12), and in public schools in which the teacher was paid by funds of the United States government except schools or institutions that are operated for profit; provided, however, that this service shall not be counted as creditable service unless the member shall pay into the retirement system a contribution equal to the full actuarial value of each year of credit for which application is made based on the salary of the member in effect at the date of application for the credit as determined by the retirement board. The retirement board shall fix and determine the time when and the conditions under which the payments shall be made.