Upon the establishment of a new school district of the first class as provided for in *RCW 28A.315.580
containing only one former first-class district, the directors of the former first-class district and two directors representative of former second-class districts selected by a majority of the board members of former second-class districts shall meet at the call of the educational service district superintendent and shall constitute the board of directors of the new district. Vacancies, once such a board has been reconstituted, shall not be filled unless the number of remaining board members is less than five, and such vacancies shall be filled in the manner otherwise provided by law.
Each board of directors so constituted shall proceed at once to organize in the manner prescribed by law and thereafter shall have all the powers and authority conferred by law upon boards of directors of first-class school districts until the next regular school election in the district at which election their successors shall be elected and qualified. At such election no more than five directors shall be elected either at large or by director districts, as the case may be, two for a term of two years and three for a term of four years: PROVIDED, That if such first-class district is in a county with a population of two hundred ten thousand or more and contains a city of the first class, two directors shall be elected for a term of three years and three directors shall be elected for a term of six years.