Section 28A. Benefits based on service in employment as defined in subsections (a) and (d) of section four A shall be payable in the same amount, on the same terms and subject to the same conditions as benefits payable on the basis of other service subject to this chapter, except that:

(a) with respect to service performed in an instructional, research, or principal administrative capacity for an educational institution, benefits shall not be paid on the basis of such services for any week commencing during the period between two successive academic years or terms, or when an agreement provides instead for a similar period between two regular but not successive terms, or during a period of paid sabbatical leave provided for in the individual's contract, to any individual if such individual performs such services in the first of such academic years or terms and if there is a contract or a reasonable assurance that such individual will perform services in any such capacity for any educational institution in the second of such academic years or terms;

(b) with respect to services performed in any other capacity for an educational institution, benefits shall not be paid on the basis of such services to any individual for any week commencing during a period between two successive academic years or terms if such individual performs such services in the first of such academic years or terms and there is a reasonable assurance that such individual will perform such services in the second of such academic years or terms; provided that, if such individual was not offered an opportunity to perform such services for the educational institution for the second of such academic years or terms, such individual shall be entitled to a retroactive payment of benefits for each week for which the individual filed a timely claim for benefits and for which benefits were denied solely because of a finding that such individual had reasonable assurance of performing services in the second of such academic years or terms;

(c) with respect to services described in subsections (a) and (b), benefits shall not be paid to any individual on the basis of such services for any week commencing during an established and customary vacation period or holiday recess if such individual performs such services in the period immediately before such vacation period or holiday recess, and there is a reasonable assurance that such individual will perform such services in the period immediately following such vacation period or holiday recess;

(d) with respect to any services described in subsections (a) and (b) benefits shall not be paid as specified in subsections (a), (b), and (c) to any individual who performed such services in an educational institution while in the employ of an educational service agency, and for the purpose of this clause the term ''educational service agency'' means a governmental agency or governmental entity, including an educational collaborative board established by section four E of chapter forty, which is established and operated exclusively for the purpose of providing such services to one or more educational institutions.