Notwithstanding any other provision of this code to the contrary, seniority for professional personnel as defined in section one, article one, chapter eighteen-a of this code shall be calculated pursuant to the provisions of section seven-a of this article as well as the following: Provided, That any recalculation of seniority of a professional personnel employee that may be required in order to remain consistent with the provisions contained herein shall be calculated retroactively, but shall not be utilized for the purposes of reversing any decision that has been made or grievance that has been filed prior to the effective date of this section:

(a) A professional employee shall begin to accrue seniority upon commencement of the employee's duties.

(b) An employee shall receive seniority credit for each day the employee is professionally employed regardless of whether the employee receives pay for that day: Provided, That no employee shall receive seniority credit for any day the employee is suspended without pay pursuant to section eight, article two of this chapter: Provided, however, That an employee who is on an approved leave of absence shall accrue seniority during the period of time that the employee is on the approved leave of absence.

(c) Any professional employee whose employment with a county board of education is terminated either voluntarily or through a reduction-in-force shall, upon reemployment with the same Board of Education in a regular full-time position, receive credit for all seniority previously accumulated with the board of Education at the date the employee's employment was terminated.

(d) Any professional employee whose employment has been terminated through reduction in force and whose name is on the preferred recall list shall retain all accumulated seniority for the purpose of seeking reemployment with the county from which he or she was terminated and nothing in this section may be construed to the contrary.

(e) Any professional employee employed for a full employment term but in a part-time position shall receive seniority credit for each day of employment prorated to the proportion of a full employment day the employee is required to work: Provided, That nothing herein allows a regular full-time employee to be credited with less than a full day of seniority credit for each day the employee is employed by the board: Provided, however, That this calculation of seniority for part-time professional personnel is prospective and does not reduce any seniority credit accumulated by any employee prior to the effective date of this section: Provided further, That for the purposes of this section a part-time employee shall be defined as an employee who is employed less than three and one-half hours per day.