(a)(1) A member shall receive a month of credited service for each month of service, from September to June, inclusive, as a teacher, provided the member makes the mandatory contribution for each month. Ten months of credited service shall be deemed to be one year of credited service. A member may not accumulate more than one year of credited service during any school year.

(2) The board may grant a member a month of credited service for a month during which such member was employed after the first school day but not later than the fifth school day of such month if (A) such month was the member’s first month of service as a teacher, (B) such month of credited service is needed by the member in order to qualify for a normal retirement benefit, and (C) the mandatory contribution for such month is paid.

(b) Any member may purchase, as provided in subsection (c) of this section, additional credited service, but not to exceed an aggregate of one year in the case of service described in subdivision (2) of this subsection for each two years of active full-time service as a Connecticut teacher; and not to exceed an aggregate of one year in the case of absence described in subdivision (8) of this subsection for each five years of active full-time service as a Connecticut teacher, provided if any such absence exceeds thirty consecutive school months, such additional credited service shall be limited to thirty school months; and not to exceed an aggregate of ten years for all service described in this subsection, except for service described in subdivision (2) of this subsection. In no event may any service described in this subsection be purchased if the member is receiving or is, or will become, entitled to receive a retirement benefit based upon such service from any governmental system other than the teachers’ retirement system or the federal Social Security System. Additional credited service includes:

(1) Service as a teacher in a school for military dependents established by the United States Department of Defense;

(2) Service as a teacher in a public school of another state of the United States, its territories or possessions;

(3) Service in the armed forces of the United States in time of war, as defined in § 27-103, or service in said armed forces during the period beginning October 27, 1953, and ending January 31, 1955;

(4) Service in a permanent full-time position for the state;

(5) Service as a teacher at The University of Connecticut prior to July 1, 1965;

(6) Service as a teacher at the Wheeler School and Library, North Stonington, prior to September 1, 1949;

(7) Service as a teacher at the Gilbert Home, Winsted, prior to September 1, 1948;

(8) Any formal leave of absence as provided in regulations adopted by the board, if the member subsequently returns to service for at least one school year;

(9) Service as a teacher at the American School for the Deaf, the Connecticut Institute for the Blind or the Newington Children’s Hospital;

(10) Forty or more days of service as a substitute teacher, or the equivalent service rendered at less than half-time, in a single public school system within the state of Connecticut in any school year, provided (A) eighteen days of such service shall equal one month of credited service under subsection (a) of this section, and (B) on and after July 1, 2022, such days of service shall be rendered within one school year;

(11) Service in the armed forces of the United States, other than service described in subdivision (3) of this subsection, not to exceed thirty months;

(12) Service as a full-time, salaried, elected official of the state or any political subdivision of the state during the 1978 calendar year or thereafter, if such member subsequently returns to service as a teacher in a public school for at least one school year;

(13) Service in the public schools of Connecticut as a member of the federal Teacher Corps, not to exceed two years;

(14) Service in the United States Peace Corps;

(15) Service in the United States VISTA (Volunteers in Service to America) program;

(16) Service in the public schools of Connecticut as a social work assistant, from January 1, 1969, to December 31, 1986, inclusive, if such member became a certified school social worker and remained in service in the public schools of Connecticut as a social worker after certification; and

(17) Service prior to July 1, 2007, as a member of the staff of the State Education Resource Center established pursuant to § 10-4q of the general statutes, revision of 1958, revised to January 1, 2007, employed in a professional capacity while possessing a certificate or permit issued by the State Board of Education.

(c) Credited service described in subdivisions (3), (8) and (10) of subsection (b) of this section shall be deemed to be service in the public schools of Connecticut.

(d) Additional credited service shall be purchased by a member (1) prior to the effective date of such member’s retirement, or (2) at the time a surviving spouse elects benefits under the provisions of subsection (d) of § 10-183h. Any purchase of such service shall be accomplished by the member paying to the board an amount determined on the basis of actuarial factors adopted by the board that reflect the present value of one-half of the full actuarial cost of the benefit increase that will be derived by the purchase of such service, except that in the case of purchase of service described in subdivision (17) of subsection (b) of this section, or in the case of purchase of service described in subdivision (2) of said subsection (b) in excess of ten years, the present value of the full actuarial cost. Such factors shall consider the member’s age at the time of purchase, actual or projected salary, and the earliest date on which the member would be eligible for a normal retirement allowance. Payments for additional credited service may be made in a lump sum by transfer of funds from the member’s accumulated one per cent contributions withheld prior to July 1, 1989, with credited interest and accumulated voluntary contributions with credited interest plus such other amounts as may be required to complete the purchase.

(e) For purposes of computing benefit amounts under § 10-183g, whole months of credited service, including additional credited service, in excess of whole years shall be used in determining aggregate accumulations of credited service.

(f) Any member who has been elected to a full-time or part-time position in an organization which has been duly designated as the teachers’ representative or who has been elected to a full-time or part-time position in a state-wide, national or international bargaining organization may, during the time such member so serves, continue membership and may make, or have made for such member, payments of contributions for such time, provided the organization which such member represents shall pay the full actuarial cost that would otherwise be incurred by the state for the time such member serves in excess of one year. If payment is made during such periods or at any time before retirement, such member shall receive credit for such service and shall be considered as serving as a teacher in the the public schools of Connecticut for the purpose of computing length of service, and for the purpose of computing average annual salary, and shall be considered by the retirement board as though such member were remaining in such member’s latest teaching position.