Idaho Code § 59-1375

A person who became an annuitant of the teachers system on or after March 29, 1965, and who had met the requirements for service or disability retirement on the date such person became an annuitant, except for the requirement of six (6) months of membership service, shall be eligible for service or disability retirement on January 1, 1968 by contributing to the employee system pursuant to rules of the board an amount equal to the sum such person would have contributed during six (6) months of membership service computed on the basis of the salary such person received on the date such person became an annuitant. This contribution shall be in lieu of the requirement of six (6) months of membership service. The amount so contributed shall not be included in the computation of disability or service retirement allowance.