(a) A county board shall make decisions affecting promotions and the filling of any service personnel positions of employment or jobs occurring throughout the school year that are to be performed by service personnel as provided in section eight of this article, on the basis of seniority, qualifications and evaluation of past service.
(b) Qualifications means the applicant holds a classification title in his or her category of employment as provided in this section and is given first opportunity for promotion and filling vacancies. Other employees then shall be considered and shall qualify by meeting the definition of the job title that relates to the promotion or vacancy, as defined in section eight of this article. If requested by the employee, the county board shall show valid cause why a service person with the most seniority is not promoted or employed in the position for which he or she applies. Qualified applicants shall be considered in the following order:
(1) Regularly employed service personnel who hold a classification title within the classification category of the vacancy;